Paste non-file-based images in clipboard as img tag

This patch converts a non-file-based image in clipboard to
an <img> tag with data URL when pasting to an editing host.

The generated markup matches |URLToImageMarkup| and the one
Firefox generates for the same case.

In addition to the unittests, manually tested by taking
screenshots to clipboard by pressing Alt+PrtScrn key on
Windows and confirmed:
* Pastable to `contenteditable`.
* Pastable to `-webkit-user-modify: read-write`.
* Not pastable to `<input>`, `<textarea>`, nor to
  `-webkit-user-modify: read-write-plaintext-only`.

Bug: 1008927
Change-Id: I19c17591567ad150575ed15af7743e819eaeb67e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2086463
Commit-Queue: Yoshifumi Inoue <yosin@chromium.org>
Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#750463}

third_party/blink/renderer/core/clipboard/clipboard_utilities.cc

@@ -31,10 +31,13 @@
 #include "third_party/blink/renderer/core/clipboard/clipboard_utilities.h"
 
 #include "net/base/escape.h"
+#include "third_party/blink/renderer/platform/image-encoders/image_encoder.h"
 #include "third_party/blink/renderer/platform/weborigin/kurl.h"
+#include "third_party/blink/renderer/platform/wtf/text/base64.h"
 #include "third_party/blink/renderer/platform/wtf/text/string_builder.h"
 #include "third_party/blink/renderer/platform/wtf/text/string_utf8_adaptor.h"
 #include "third_party/blink/renderer/platform/wtf/text/wtf_string.h"
+#include "third_party/skia/include/encode/SkPngEncoder.h"
 
 namespace blink {
 
@@ -90,4 +93,28 @@ String URLToImageMarkup(const KURL& url, const String& title) {
   return builder.ToString();
 }
 
+String BitmapToImageMarkup(const SkBitmap& bitmap) {
+  if (bitmap.isNull())
+    return String();
+
+  // Encode bitmap to Vector<uint8_t> on the main thread.
+  SkPixmap pixmap;
+  bitmap.peekPixels(&pixmap);
+
+  // Set encoding options to favor speed over size.
+  SkPngEncoder::Options options;
+  options.fZLibLevel = 1;
+  options.fFilterFlags = SkPngEncoder::FilterFlag::kNone;
+
+  Vector<uint8_t> png_data;
+  if (!ImageEncoder::Encode(&png_data, pixmap, options))
+    return String();
+
+  StringBuilder markup;
+  markup.Append("<img src=\"data:image/png;base64,");
+  markup.Append(Base64Encode(png_data));
+  markup.Append("\" alt=\"\"/>");
+  return markup.ToString();
+}
+
 }  // namespace blink

third_party/blink/renderer/core/clipboard/clipboard_utilities.h

@@ -35,6 +35,7 @@
 #include "third_party/blink/renderer/core/core_export.h"
 #include "third_party/blink/renderer/platform/weborigin/kurl.h"
 #include "third_party/blink/renderer/platform/wtf/forward.h"
+#include "third_party/skia/include/core/SkBitmap.h"
 
 namespace blink {
 
@@ -44,6 +45,7 @@ CORE_EXPORT void ReplaceNewlinesWithWindowsStyleNewlines(String&);
 CORE_EXPORT void ReplaceNBSPWithSpace(String&);
 CORE_EXPORT String ConvertURIListToURL(const String& uri_list);
 CORE_EXPORT String URLToImageMarkup(const KURL&, const String& title);
+CORE_EXPORT String BitmapToImageMarkup(const SkBitmap& bitmap);
 
 }  // namespace blink
 

third_party/blink/renderer/core/clipboard/clipboard_utilities_test.cc

@@ -43,4 +43,17 @@ TEST(ClipboardUtilitiesTest, URLToImageMarkupEmbeddedNull) {
           String(kTitleWithNull, sizeof(kTitleWithNull) - 1)));
 }
 
+TEST(ClipboardUtilitiesTest, BitmapToImageMarkupEmpty) {
+  SkBitmap bitmap;
+  EXPECT_TRUE(BitmapToImageMarkup(bitmap).IsNull());
+}
+
+TEST(ClipboardUtilitiesTest, BitmapToImageMarkup) {
+  SkBitmap bitmap;
+  bitmap.allocPixels(SkImageInfo::MakeN32Premul(10, 5));
+  EXPECT_EQ(
+      R"HTML(<img src="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAoAAAAFCAYAAAB8ZH1oAAAADElEQVQYGWNgGEYAAADNAAGVVebMAAAAAElFTkSuQmCC" alt=""/>)HTML",
+      BitmapToImageMarkup(bitmap));
+}
+
 }  // namespace blink

third_party/blink/renderer/core/clipboard/system_clipboard.cc

@@ -152,6 +152,12 @@ SkBitmap SystemClipboard::ReadImage(mojom::ClipboardBuffer buffer) {
   return image;
 }
 
+String SystemClipboard::ReadImageAsImageMarkup(
+    mojom::blink::ClipboardBuffer buffer) {
+  SkBitmap bitmap = ReadImage(buffer);
+  return BitmapToImageMarkup(bitmap);
+}
+
 void SystemClipboard::WriteImageWithTag(Image* image,
                                                 const KURL& url,
                                                 const String& title) {

third_party/blink/renderer/core/clipboard/system_clipboard.h

@@ -58,6 +58,7 @@ class CORE_EXPORT SystemClipboard final
   String ReadRTF();
 
   SkBitmap ReadImage(mojom::ClipboardBuffer);
+  String ReadImageAsImageMarkup(mojom::blink::ClipboardBuffer);
 
   // Write the image and its associated tag (bookmark/HTML types).
   void WriteImageWithTag(Image*, const KURL&, const String& title);

third_party/blink/renderer/core/editing/commands/clipboard_commands.cc

@@ -373,6 +373,15 @@ ClipboardCommands::GetFragmentFromClipboard(LocalFrame& frame) {
   if (fragment)
     return std::make_pair(fragment, false);
 
+  if (const String markup = frame.GetSystemClipboard()->ReadImageAsImageMarkup(
+          mojom::blink::ClipboardBuffer::kStandard)) {
+    fragment = CreateFragmentFromMarkup(*frame.GetDocument(), markup,
+                                        /* base_url */ "",
+                                        kDisallowScriptingAndPluginContent);
+    DCHECK(fragment);
+    return std::make_pair(fragment, false);
+  }
+
   const String text = frame.GetSystemClipboard()->ReadPlainText();
   if (text.IsEmpty())
     return std::make_pair(fragment, false);