Android Video Thumbnail: Hook video thumbnail backend to UI.

This CL hooks the video thumbnail backend to the UI layer of new
download home.

Bug: 826021
Change-Id: I190ad09e8231d94d7546128bd1d22dc39f4d5f35
Reviewed-on: https://chromium-review.googlesource.com/1247529
Commit-Queue: Xing Liu <xingliu@chromium.org>
Reviewed-by: David Trainor <dtrainor@chromium.org>
Cr-Commit-Position: refs/heads/master@{#595706}

chrome/android/java/res_download/layout/download_manager_video_item.xml

@@ -19,7 +19,7 @@
         android:id="@+id/thumbnail"
         android:layout_width="match_parent"
         android:layout_height="200dp"
-        android:scaleType="centerInside"
+        android:scaleType="centerCrop"
         android:adjustViewBounds="true"
         app:layout_column="0"
         app:layout_row="0"

chrome/android/java/src/org/chromium/chrome/browser/download/DownloadMediaParserBridge.java

@@ -19,9 +19,9 @@ public class DownloadMediaParserBridge {
      * @param totalSize Total size of the media file.
      * @param callback Callback to get the result.
      */
-    public DownloadMediaParserBridge(String mimeType, String filePath, long totalSize,
-            Callback<DownloadMediaData> callback) {
-        mNativeDownloadMediaParserBridge = nativeInit(mimeType, filePath, totalSize, callback);
+    public DownloadMediaParserBridge(
+            String mimeType, String filePath, Callback<DownloadMediaData> callback) {
+        mNativeDownloadMediaParserBridge = nativeInit(mimeType, filePath, callback);
     }
 
     /**
@@ -43,7 +43,7 @@ public class DownloadMediaParserBridge {
     }
 
     private native long nativeInit(
-            String mimeType, String filePath, long totalSize, Callback<DownloadMediaData> callback);
+            String mimeType, String filePath, Callback<DownloadMediaData> callback);
     private native void nativeDestory(long nativeDownloadMediaParserBridge);
     private native void nativeStart(long nativeDownloadMediaParserBridge);
 }

chrome/android/java/src/org/chromium/chrome/browser/download/home/glue/ThumbnailRequestGlue.java

@@ -7,14 +7,17 @@ package org.chromium.chrome.browser.download.home.glue;
 import android.graphics.Bitmap;
 
 import org.chromium.base.Callback;
+import org.chromium.chrome.browser.widget.ThumbnailProvider;
 import org.chromium.chrome.browser.widget.ThumbnailProvider.ThumbnailRequest;
+import org.chromium.chrome.browser.widget.ThumbnailProviderImpl;
+import org.chromium.components.offline_items_collection.OfflineContentProvider;
 import org.chromium.components.offline_items_collection.OfflineItem;
 import org.chromium.components.offline_items_collection.OfflineItemVisuals;
 import org.chromium.components.offline_items_collection.VisualsCallback;
 
 /**
  * Glue class responsible for connecting the current downloads and {@link OfflineContentProvider}
- * thumbnail work to the {@link ThumbnailProvider} via a custon {@link ThumbnailProviderImpl}.
+ * thumbnail work to the {@link ThumbnailProvider} via a custom {@link ThumbnailProviderImpl}.
  */
 public class ThumbnailRequestGlue implements ThumbnailRequest {
     private final OfflineContentProviderGlue mProvider;
@@ -39,6 +42,11 @@ public class ThumbnailRequestGlue implements ThumbnailRequest {
         return mItem.filePath;
     }
 
+    @Override
+    public String getMimeType() {
+        return mItem.mimeType;
+    }
+
     @Override
     public String getContentId() {
         return mItem.id.id;

chrome/android/java/src/org/chromium/chrome/browser/download/home/list/UiUtils.java

@@ -117,9 +117,7 @@ public final class UiUtils {
     public static boolean canHaveThumbnails(OfflineItem item) {
         switch (item.filter) {
             case OfflineItemFilter.FILTER_PAGE:
-            // TODO(shaktisahu, xingliu): Remove this after video thumbnail generation pipeline is
-            // done.
-            // case OfflineItemFilter.FILTER_VIDEO:
+            case OfflineItemFilter.FILTER_VIDEO:
             case OfflineItemFilter.FILTER_IMAGE:
                 return true;
             default:

chrome/android/java/src/org/chromium/chrome/browser/download/ui/DownloadItemView.java

@@ -178,6 +178,11 @@ public class DownloadItemView extends SelectableItemView<DownloadHistoryItemWrap
         return mItem == null ? null : mItem.getFilePath();
     }
 
+    @Override
+    public String getMimeType() {
+        return mItem == null ? null : mItem.getMimeType();
+    }
+
     @Override
     public @Nullable String getContentId() {
         return mItem == null ? "" : mItem.getId();

chrome/android/java/src/org/chromium/chrome/browser/suggestions/ImageFetcher.java

@@ -390,5 +390,10 @@ public class ImageFetcher {
         public Promise<Bitmap> getPromise() {
             return mThumbnailReceivedPromise;
         }
+
+        @Override
+        public String getMimeType() {
+            return null;
+        }
     }
 }

chrome/android/java/src/org/chromium/chrome/browser/widget/ThumbnailGenerator.java

@@ -42,7 +42,7 @@ public class ThumbnailGenerator {
         boolean hasFilePath = !TextUtils.isEmpty(request.getFilePath());
         assert hasFilePath;
         nativeRetrieveThumbnail(getNativeThumbnailGenerator(), request.getContentId(),
-                request.getFilePath(), request.getIconSize(), callback);
+                request.getFilePath(), request.getMimeType(), request.getIconSize(), callback);
     }
 
     /**
@@ -80,5 +80,6 @@ public class ThumbnailGenerator {
     private native long nativeInit();
     private native void nativeDestroy(long nativeThumbnailGenerator);
     private native void nativeRetrieveThumbnail(long nativeThumbnailGenerator, String contentId,
-            String filePath, int thumbnailSize, ThumbnailGeneratorCallback callback);
+            String filePath, String mimeType, int thumbnailSize,
+            ThumbnailGeneratorCallback callback);
 }

chrome/android/java/src/org/chromium/chrome/browser/widget/ThumbnailProvider.java

@@ -20,6 +20,10 @@ public interface ThumbnailProvider {
         @Nullable
         String getFilePath();
 
+        /** The mime type of the file. */
+        @Nullable
+        String getMimeType();
+
         /** Content ID that uniquely identifies the file. */
         @Nullable
         String getContentId();

chrome/android/javatests/src/org/chromium/chrome/browser/download/DownloadMediaParserTest.java

@@ -63,7 +63,7 @@ public class DownloadMediaParserTest {
         // The native DownloadMediaParser needs to be created on UI thread.
         ThreadUtils.runOnUiThreadBlocking(() -> {
             DownloadMediaParserBridge parser = new DownloadMediaParserBridge(
-                    mimeType, filePath, mediaFile.length(), (DownloadMediaData mediaData) -> {
+                    mimeType, filePath, (DownloadMediaData mediaData) -> {
                         result.mediaData = mediaData;
                         result.done = true;
                     });

chrome/android/javatests/src/org/chromium/chrome/browser/widget/ThumbnailDiskStorageTest.java

@@ -63,6 +63,11 @@ public class ThumbnailDiskStorageTest {
             return null;
         }
 
+        @Override
+        public String getMimeType() {
+            return null;
+        }
+
         @Override
         public String getContentId() {
             return mContentId;

chrome/android/javatests/src/org/chromium/chrome/browser/widget/ThumbnailProviderImplTest.java

@@ -188,6 +188,11 @@ public class ThumbnailProviderImplTest {
             return mTestFilePath;
         }
 
+        @Override
+        public String getMimeType() {
+            return null;
+        }
+
         @Override
         public @Nullable String getContentId() {
             return "contentId"; // None-null value for ThumbnailProviderImpl to work

chrome/browser/BUILD.gn

@@ -455,6 +455,8 @@ jumbo_split_static_library("browser") {
     "download/offline_item_utils.h",
     "download/save_package_file_picker.cc",
     "download/save_package_file_picker.h",
+    "download/thumbnail_util.cc",
+    "download/thumbnail_util.h",
     "download/trusted_sources_manager.cc",
     "download/trusted_sources_manager.h",
     "download/trusted_sources_manager_win.cc",

chrome/browser/android/download/download_media_parser.cc

@@ -6,9 +6,11 @@
 
 #include "base/bind.h"
 #include "base/files/file.h"
+#include "base/files/file_util.h"
 #include "base/numerics/safe_conversions.h"
 #include "base/task/post_task.h"
 #include "base/task/task_traits.h"
+#include "base/task_runner_util.h"
 #include "cc/paint/skia_paint_canvas.h"
 #include "chrome/browser/android/download/local_media_data_source_factory.h"
 #include "content/public/browser/android/gpu_video_accelerator_factories_provider.h"
@@ -38,19 +40,23 @@ bool IsSupportedMediaMimeType(const std::string& mime_type) {
 void OnRequestOverlayInfo(bool decoder_requires_restart_for_overlay,
                           const media::ProvideOverlayInfoCB& overlay_info_cb) {
   // No android overlay associated with video thumbnail.
+  if (overlay_info_cb)
     overlay_info_cb.Run(media::OverlayInfo());
 }
 
+int64_t GetFileSize(const base::FilePath& file_path) {
+  int64_t size = 0;
+  if (!base::GetFileSize(file_path, &size))
+    return -1;
+  return size;
+}
+
 }  // namespace
 
-DownloadMediaParser::DownloadMediaParser(int64_t size,
-                                         const std::string& mime_type,
-                                         const base::FilePath& file_path,
-                                         ParseCompleteCB parse_complete_cb)
-    : size_(size),
-      mime_type_(mime_type),
+DownloadMediaParser::DownloadMediaParser(const std::string& mime_type,
+                                         const base::FilePath& file_path)
+    : mime_type_(mime_type),
       file_path_(file_path),
-      parse_complete_cb_(std::move(parse_complete_cb)),
       file_task_runner_(
           base::CreateSingleThreadTaskRunnerWithTraits({base::MayBlock()})),
       decode_done_(false),
@@ -58,13 +64,30 @@ DownloadMediaParser::DownloadMediaParser(int64_t size,
 
 DownloadMediaParser::~DownloadMediaParser() = default;
 
-void DownloadMediaParser::Start() {
+void DownloadMediaParser::Start(ParseCompleteCB parse_complete_cb) {
+  parse_complete_cb_ = std::move(parse_complete_cb);
+
   // Only process media mime types.
   if (!IsSupportedMediaMimeType(mime_type_)) {
     OnError();
     return;
   }
 
+  // Get the size of the file if needed.
+  base::PostTaskAndReplyWithResult(
+      file_task_runner_.get(), FROM_HERE,
+      base::BindOnce(&GetFileSize, file_path_),
+      base::BindOnce(&DownloadMediaParser::OnReadFileSize,
+                     weak_factory_.GetWeakPtr()));
+}
+
+void DownloadMediaParser::OnReadFileSize(int64_t file_size) {
+  if (file_size < 0) {
+    OnError();
+    return;
+  }
+
+  size_ = file_size;
   RetrieveMediaParser(
       content::ServiceManagerConnection::GetForProcess()->GetConnector());
 }
@@ -188,6 +211,7 @@ void DownloadMediaParser::DecodeVideoFrame() {
 
   decoder_->Start(base::BindOnce(&DownloadMediaParser::OnVideoFrameDecoded,
                                  weak_factory_.GetWeakPtr()));
+  video_frame_data_.reset();
 }
 
 void DownloadMediaParser::OnVideoFrameDecoded(

chrome/browser/android/download/download_media_parser.h

@@ -34,9 +34,9 @@ class SkBitmap;
 // Parse local media files, including media metadata and thumbnails.
 // Metadata is always parsed in utility process for both audio and video files.
 //
-// For video file, the thumbnail may be poster image in metadata or extracted
-// video frame. The frame extraction always happens in utility process. The
-// decoding may happen in utility or GPU process based on video codec.
+// For video file, the thumbnail will be the a video key frame. The frame
+// extraction always happens in utility process. The decoding may happen in
+// utility or GPU process based on video codec.
 class DownloadMediaParser : public MediaParserProvider, public media::MediaLog {
  public:
   using ParseCompleteCB =
@@ -44,19 +44,19 @@ class DownloadMediaParser : public MediaParserProvider, public media::MediaLog {
                               chrome::mojom::MediaMetadataPtr media_metadata,
                               SkBitmap bitmap)>;
 
-  DownloadMediaParser(int64_t size,
-                      const std::string& mime_type,
-                      const base::FilePath& file_path,
-                      ParseCompleteCB parse_complete_cb);
+  DownloadMediaParser(const std::string& mime_type,
+                      const base::FilePath& file_path);
   ~DownloadMediaParser() override;
 
-  // Parse media metadata in a local file. All file IO will run on
+  // Parse media metadata and thumbnail in a local file. All file IO will run on
   // |file_task_runner|. The metadata is parsed in an utility process safely.
   // The thumbnail is retrieved from GPU process or utility process based on
   // different codec.
-  void Start();
+  void Start(ParseCompleteCB parse_complete_cb);
 
  private:
+  void OnReadFileSize(int64_t file_size);
+
   // MediaParserProvider implementation:
   void OnMediaParserCreated() override;
   void OnConnectionError() override;

chrome/browser/android/download/download_media_parser_bridge.cc

@@ -47,7 +47,6 @@ jlong JNI_DownloadMediaParserBridge_Init(
     const base::android::JavaParamRef<jobject>& jcaller,
     const base::android::JavaParamRef<jstring>& jmime_type,
     const base::android::JavaParamRef<jstring>& jfile_path,
-    jlong jtotal_size,
     const base::android::JavaParamRef<jobject>& jcallback) {
   base::FilePath file_path(
       base::android::ConvertJavaStringToUTF8(env, jfile_path));
@@ -55,22 +54,18 @@ jlong JNI_DownloadMediaParserBridge_Init(
       base::android::ConvertJavaStringToUTF8(env, jmime_type);
 
   auto* bridge = new DownloadMediaParserBridge(
-      static_cast<int64_t>(jtotal_size), mime_type, file_path,
+      mime_type, file_path,
       base::BindOnce(&OnMediaParsed,
                      base::android::ScopedJavaGlobalRef<jobject>(jcallback)));
   return reinterpret_cast<intptr_t>(bridge);
 }
 
 DownloadMediaParserBridge::DownloadMediaParserBridge(
-    int64_t size,
     const std::string& mime_type,
     const base::FilePath& file_path,
     DownloadMediaParser::ParseCompleteCB parse_complete_cb)
-    : parser_(std::make_unique<DownloadMediaParser>(
-          size,
-          mime_type,
-          file_path,
-          std::move(parse_complete_cb))) {}
+    : parser_(std::make_unique<DownloadMediaParser>(mime_type, file_path)),
+      parse_complete_cb_(std::move(parse_complete_cb)) {}
 
 DownloadMediaParserBridge::~DownloadMediaParserBridge() = default;
 
@@ -79,5 +74,5 @@ void DownloadMediaParserBridge::Destory(JNIEnv* env, jobject obj) {
 }
 
 void DownloadMediaParserBridge::Start(JNIEnv* env, jobject obj) {
-  parser_->Start();
+  parser_->Start(std::move(parse_complete_cb_));
 }

chrome/browser/android/download/download_media_parser_bridge.h

@@ -19,7 +19,6 @@ class DownloadMediaParser;
 class DownloadMediaParserBridge {
  public:
   DownloadMediaParserBridge(
-      int64_t size,
       const std::string& mime_type,
       const base::FilePath& file_path,
       DownloadMediaParser::ParseCompleteCB parse_complete_cb);
@@ -31,6 +30,7 @@ class DownloadMediaParserBridge {
  private:
   // The media parser that does actual jobs in a sandboxed process.
   std::unique_ptr<DownloadMediaParser> parser_;
+  DownloadMediaParser::ParseCompleteCB parse_complete_cb_;
 
   DISALLOW_COPY_AND_ASSIGN(DownloadMediaParserBridge);
 };

chrome/browser/android/widget/thumbnail_generator.cc

@@ -8,6 +8,8 @@
 
 #include "base/android/jni_string.h"
 #include "base/threading/thread_restrictions.h"
+#include "chrome/browser/android/download/download_media_parser.h"
+#include "chrome/browser/download/thumbnail_util.h"
 #include "content/public/browser/browser_thread.h"
 #include "jni/ThumbnailGenerator_jni.h"
 #include "ui/gfx/android/java_bitmap.h"
@@ -15,6 +17,30 @@
 class SkBitmap;
 
 using base::android::JavaParamRef;
+using base::android::ScopedJavaGlobalRef;
+
+namespace {
+
+void ForwardJavaCallback(const ScopedJavaGlobalRef<jobject>& java_delegate,
+                         const ScopedJavaGlobalRef<jstring>& content_id,
+                         int icon_size,
+                         const ScopedJavaGlobalRef<jobject>& callback,
+                         SkBitmap thumbnail) {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
+  JNIEnv* env = base::android::AttachCurrentThread();
+  Java_ThumbnailGenerator_onThumbnailRetrieved(
+      env, java_delegate, content_id, icon_size,
+      thumbnail.drawsNothing() ? NULL : gfx::ConvertToJavaBitmap(&thumbnail),
+      callback);
+}
+
+void OnThumbnailScaled(base::OnceCallback<void(SkBitmap)> java_callback,
+                       SkBitmap scaled_thumbnail) {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
+  std::move(java_callback).Run(std::move(scaled_thumbnail));
+}
+
+}  // namespace
 
 ThumbnailGenerator::ThumbnailGenerator(const JavaParamRef<jobject>& jobj)
     : java_delegate_(jobj), weak_factory_(this) {
@@ -29,19 +55,27 @@ void ThumbnailGenerator::Destroy(JNIEnv* env,
   delete this;
 }
 
-void ThumbnailGenerator::OnThumbnailRetrieved(
-    const base::android::ScopedJavaGlobalRef<jstring>& content_id,
-    int icon_size,
-    const base::android::ScopedJavaGlobalRef<jobject>& callback,
+void ThumbnailGenerator::OnImageThumbnailRetrieved(
+    base::OnceCallback<void(SkBitmap)> java_callback,
     const SkBitmap& thumbnail) {
   DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
 
   // Send the bitmap back to Java-land.
-  JNIEnv* env = base::android::AttachCurrentThread();
-  Java_ThumbnailGenerator_onThumbnailRetrieved(
-      env, java_delegate_, content_id, icon_size,
-      thumbnail.drawsNothing() ? NULL : gfx::ConvertToJavaBitmap(&thumbnail),
-      callback);
+  std::move(java_callback).Run(std::move(thumbnail));
+}
+
+void ThumbnailGenerator::OnVideoThumbnailRetrieved(
+    base::OnceCallback<void(SkBitmap)> java_callback,
+    int icon_size,
+    std::unique_ptr<DownloadMediaParser> parser,
+    bool success,
+    chrome::mojom::MediaMetadataPtr media_metadata,
+    SkBitmap thumbnail) {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
+
+  // Scale the bitmap before sending back to Java.
+  ScaleDownBitmap(icon_size, std::move(thumbnail),
+                  base::BindOnce(&OnThumbnailScaled, std::move(java_callback)));
 }
 
 void ThumbnailGenerator::RetrieveThumbnail(
@@ -49,20 +83,42 @@ void ThumbnailGenerator::RetrieveThumbnail(
     const JavaParamRef<jobject>& jobj,
     const JavaParamRef<jstring>& jcontent_id,
     const JavaParamRef<jstring>& jfile_path,
+    const JavaParamRef<jstring>& jmime_type,
     jint icon_size,
     const JavaParamRef<jobject>& callback) {
   DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
 
-  std::string file_path =
-      base::android::ConvertJavaStringToUTF8(env, jfile_path);
+  base::FilePath file_path = base::FilePath::FromUTF8Unsafe(
+      base::android::ConvertJavaStringToUTF8(env, jfile_path));
+
+  std::string mime_type =
+      jmime_type.is_null()
+          ? ""
+          : base::android::ConvertJavaStringToUTF8(env, jmime_type);
+
+  // Bind everything passed back to Java.
+  auto java_callback =
+      base::BindOnce(&ForwardJavaCallback, java_delegate_,
+                     ScopedJavaGlobalRef<jstring>(jcontent_id), icon_size,
+                     ScopedJavaGlobalRef<jobject>(callback));
+
+  // Retrieve video thumbnail.
+  if (base::StartsWith(mime_type, "video/",
+                       base::CompareCase::INSENSITIVE_ASCII)) {
+    auto parser = std::make_unique<DownloadMediaParser>(mime_type, file_path);
+    parser->Start(base::BindOnce(&ThumbnailGenerator::OnVideoThumbnailRetrieved,
+                                 weak_factory_.GetWeakPtr(),
+                                 std::move(java_callback), icon_size,
+                                 std::move(parser)));
+    return;
+  }
 
+  // Retrieve image thumbnail.
   auto request = std::make_unique<ImageThumbnailRequest>(
       icon_size,
-      base::BindOnce(
-          &ThumbnailGenerator::OnThumbnailRetrieved, weak_factory_.GetWeakPtr(),
-          base::android::ScopedJavaGlobalRef<jstring>(jcontent_id), icon_size,
-          base::android::ScopedJavaGlobalRef<jobject>(callback)));
-  request->Start(base::FilePath::FromUTF8Unsafe(file_path));
+      base::BindOnce(&ThumbnailGenerator::OnImageThumbnailRetrieved,
+                     weak_factory_.GetWeakPtr(), std::move(java_callback)));
+  request->Start(file_path);
 
   // Dropping ownership of |request| here because it will clean itself up once
   // the started request finishes.

chrome/browser/android/widget/thumbnail_generator.h

@@ -5,11 +5,15 @@
 #ifndef CHROME_BROWSER_ANDROID_WIDGET_THUMBNAIL_GENERATOR_H_
 #define CHROME_BROWSER_ANDROID_WIDGET_THUMBNAIL_GENERATOR_H_
 
+#include <memory>
 #include <string>
 
 #include "base/android/jni_android.h"
 #include "base/memory/weak_ptr.h"
 #include "chrome/browser/download/image_thumbnail_request.h"
+#include "chrome/services/media_gallery_util/public/mojom/media_parser.mojom.h"
+
+class DownloadMediaParser;
 
 // Kicks off asynchronous pipelines for creating thumbnails for local files.
 // The native-side ThumbnailGenerator is owned by the Java-side and can be
@@ -31,19 +35,29 @@ class ThumbnailGenerator {
       const base::android::JavaParamRef<jobject>& jobj,
       const base::android::JavaParamRef<jstring>& jcontent_id,
       const base::android::JavaParamRef<jstring>& jfile_path,
+      const base::android::JavaParamRef<jstring>& jmime_type,
       jint icon_size,
       const base::android::JavaParamRef<jobject>& callback);
 
  private:
   ~ThumbnailGenerator();
 
-  // Called when the thumbnail is ready.  |thumbnail| will be empty on failure.
-  void OnThumbnailRetrieved(
-      const base::android::ScopedJavaGlobalRef<jstring>& content_id,
-      int icon_size,
-      const base::android::ScopedJavaGlobalRef<jobject>& callback,
+  // Called when the image thumbnail is ready.  |thumbnail| will be empty on
+  // failure.
+  void OnImageThumbnailRetrieved(
+      base::OnceCallback<void(SkBitmap)> java_callback,
       const SkBitmap& thumbnail);
 
+  // Called when the video thumbnail is ready.  |thumbnail| will be empty on
+  // failure.
+  void OnVideoThumbnailRetrieved(
+      base::OnceCallback<void(SkBitmap)> java_callback,
+      int icon_size,
+      std::unique_ptr<DownloadMediaParser> parser,
+      bool success,
+      chrome::mojom::MediaMetadataPtr media_metadata,
+      SkBitmap thumbnail);
+
   // This is a {@link ThumbnailGenerator} Java object.
   base::android::ScopedJavaGlobalRef<jobject> java_delegate_;
   base::WeakPtrFactory<ThumbnailGenerator> weak_factory_;

chrome/browser/download/image_thumbnail_request.cc

@@ -9,6 +9,7 @@
 #include "base/files/file_util.h"
 #include "base/task/post_task.h"
 #include "base/threading/scoped_blocking_call.h"
+#include "chrome/browser/download/thumbnail_util.h"
 #include "content/public/browser/browser_task_traits.h"
 #include "content/public/browser/browser_thread.h"
 #include "skia/ext/image_operations.h"
@@ -41,26 +42,6 @@ std::string LoadImageData(const base::FilePath& path) {
   return data;
 }
 
-SkBitmap ScaleDownBitmap(int icon_size, const SkBitmap& decoded_image) {
-  DCHECK(!content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
-
-  if (decoded_image.drawsNothing())
-    return decoded_image;
-
-  // Shrink the image down so that its smallest dimension is equal to or
-  // smaller than the requested size.
-  int min_dimension = std::min(decoded_image.width(), decoded_image.height());
-
-  if (min_dimension <= icon_size)
-    return decoded_image;
-
-  uint64_t width = static_cast<uint64_t>(decoded_image.width());
-  uint64_t height = static_cast<uint64_t>(decoded_image.height());
-  return skia::ImageOperations::Resize(
-      decoded_image, skia::ImageOperations::RESIZE_BEST,
-      width * icon_size / min_dimension, height * icon_size / min_dimension);
-}
-
 }  // namespace
 
 ImageThumbnailRequest::ImageThumbnailRequest(
@@ -87,9 +68,7 @@ void ImageThumbnailRequest::Start(const base::FilePath& path) {
 
 void ImageThumbnailRequest::OnImageDecoded(const SkBitmap& decoded_image) {
   DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
-  base::PostTaskWithTraitsAndReplyWithResult(
-      FROM_HERE, {base::MayBlock(), base::TaskPriority::USER_BLOCKING},
-      base::BindOnce(&ScaleDownBitmap, icon_size_, decoded_image),
+  ScaleDownBitmap(icon_size_, decoded_image,
                   base::BindOnce(&ImageThumbnailRequest::FinishRequest,
                                  weak_ptr_factory_.GetWeakPtr()));
 }
@@ -110,9 +89,10 @@ void ImageThumbnailRequest::OnLoadComplete(const std::string& data) {
   ImageDecoder::Start(this, data);
 }
 
-void ImageThumbnailRequest::FinishRequest(const SkBitmap& thumbnail) {
+void ImageThumbnailRequest::FinishRequest(SkBitmap thumbnail) {
   DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
-  base::PostTaskWithTraits(FROM_HERE, {content::BrowserThread::UI},
-                           base::BindOnce(std::move(callback_), thumbnail));
+  base::PostTaskWithTraits(
+      FROM_HERE, {content::BrowserThread::UI},
+      base::BindOnce(std::move(callback_), std::move(thumbnail)));
   delete this;
 }

chrome/browser/download/image_thumbnail_request.h

@@ -33,7 +33,7 @@ class ImageThumbnailRequest : public ImageDecoder::ImageRequest {
 
   void OnLoadComplete(const std::string& data);
 
-  void FinishRequest(const SkBitmap& thumbnail);
+  void FinishRequest(SkBitmap thumbnail);
 
   const int icon_size_;
   base::OnceCallback<void(const SkBitmap&)> callback_;

chrome/browser/download/thumbnail_util.cc

+// Copyright 2018 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "chrome/browser/download/thumbnail_util.h"
+
+#include "base/logging.h"
+#include "base/task/post_task.h"
+#include "content/public/browser/browser_thread.h"
+#include "skia/ext/image_operations.h"
+
+namespace {
+
+SkBitmap ScaleDownBitmapOnIOThread(int icon_size, SkBitmap bitmap) {
+  DCHECK(!content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
+
+  if (bitmap.drawsNothing())
+    return bitmap;
+
+  // Shrink the image down so that its smallest dimension is equal to or
+  // smaller than the requested size.
+  int min_dimension = std::min(bitmap.width(), bitmap.height());
+
+  if (min_dimension <= icon_size)
+    return bitmap;
+
+  uint64_t width = static_cast<uint64_t>(bitmap.width());
+  uint64_t height = static_cast<uint64_t>(bitmap.height());
+  return skia::ImageOperations::Resize(
+      bitmap, skia::ImageOperations::RESIZE_BEST,
+      width * icon_size / min_dimension, height * icon_size / min_dimension);
+}
+
+}  // namespace
+
+void ScaleDownBitmap(int icon_size,
+                     const SkBitmap& bitmap,
+                     base::OnceCallback<void(SkBitmap)> callback) {
+  DCHECK(callback);
+  DCHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
+
+  // Scale down bitmap on another thread.
+  base::PostTaskWithTraitsAndReplyWithResult(
+      FROM_HERE, {base::MayBlock(), base::TaskPriority::USER_BLOCKING},
+      base::BindOnce(&ScaleDownBitmapOnIOThread, icon_size, std::move(bitmap)),
+      std::move(callback));
+}

chrome/browser/download/thumbnail_util.h

+// Copyright 2018 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CHROME_BROWSER_DOWNLOAD_THUMBNAIL_UTIL_H_
+#define CHROME_BROWSER_DOWNLOAD_THUMBNAIL_UTIL_H_
+
+#include "base/callback.h"
+
+class SkBitmap;
+
+// Scale down the bitmap. The result is returned in the |callback|. The aspect
+// ratio is kept. The maximum size of the width or height will be no greater
+// than |icon_size|.
+void ScaleDownBitmap(int icon_size,
+                     const SkBitmap& bitmap,
+                     base::OnceCallback<void(SkBitmap)> callback);
+
+#endif  // CHROME_BROWSER_DOWNLOAD_THUMBNAIL_UTIL_H_