Fix ThumbnailProviderImpl destroy chain.

Add safety checks to the following classes to make sure they work better
during destroy:
- ThumbnailProviderImpl - Cancel all requests after destroy and do not
use any results given.
- BitmapCache - Do not add bitmaps to the cache after destroy (real
exception).
- ThumbnailDiskStorage - Do not take requests after destroy and do not
return results after destroy.

Bug: 934515
Change-Id: Id2bbac832fd4b9c81ae81ee806f66494eda59e16
Reviewed-on: https://chromium-review.googlesource.com/c/1482590
Commit-Queue: David Trainor <dtrainor@chromium.org>
Reviewed-by: Theresa <twellington@chromium.org>
Cr-Commit-Position: refs/heads/master@{#634956}

chrome/android/java/src/org/chromium/chrome/browser/BitmapCache.java

@@ -104,6 +104,8 @@ public class BitmapCache {
 
     public Bitmap getBitmap(String key) {
         ThreadUtils.assertOnUiThread();
+        if (mBitmapCache == null) return null;
+
         Bitmap cachedBitmap = getBitmapCache().get(key);
         assert cachedBitmap == null || !cachedBitmap.isRecycled();
         maybeScheduleDeduplicationCache();
@@ -112,7 +114,8 @@ public class BitmapCache {
 
     public void putBitmap(@NonNull String key, @Nullable Bitmap bitmap) {
         ThreadUtils.assertOnUiThread();
-        if (bitmap == null) return;
+        if (bitmap == null || mBitmapCache == null) return;
+
         if (!SysUtils.isLowEndDevice()) getBitmapCache().put(key, bitmap);
         maybeScheduleDeduplicationCache();
         sDeduplicationCache.put(key, new WeakReference<>(bitmap));

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

@@ -83,6 +83,9 @@ public class ThumbnailDiskStorage implements ThumbnailGeneratorCallback {
     @VisibleForTesting
     long mSizeBytes;
 
+    // Whether or not this class has been destroyed and should not be used.
+    private boolean mDestroyed;
+
     private class InitTask extends AsyncTask<Void> {
         @Override
         protected Void doInBackground() {
@@ -201,6 +204,7 @@ public class ThumbnailDiskStorage implements ThumbnailGeneratorCallback {
      */
     public void destroy() {
         mThumbnailGenerator.destroy();
+        mDestroyed = true;
     }
 
     /**
@@ -217,7 +221,7 @@ public class ThumbnailDiskStorage implements ThumbnailGeneratorCallback {
      */
     public void retrieveThumbnail(ThumbnailProvider.ThumbnailRequest request) {
         ThreadUtils.assertOnUiThread();
-        if (TextUtils.isEmpty(request.getContentId())) return;
+        if (mDestroyed || TextUtils.isEmpty(request.getContentId())) return;
 
         new GetThumbnailTask(request).executeOnExecutor(AsyncTask.SERIAL_EXECUTOR);
     }
@@ -233,6 +237,9 @@ public class ThumbnailDiskStorage implements ThumbnailGeneratorCallback {
     @Override
     public void onThumbnailRetrieved(
             @NonNull String contentId, @Nullable Bitmap bitmap, int iconSizePx) {
+        // If we've been destroyed, drop any responses coming back from retrieval tasks.
+        if (mDestroyed) return;
+
         ThreadUtils.assertOnUiThread();
         if (bitmap != null && !TextUtils.isEmpty(contentId)) {
             new CacheThumbnailTask(contentId, bitmap, iconSizePx)

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

@@ -84,6 +84,10 @@ public class ThumbnailProviderImpl implements ThumbnailProvider, ThumbnailStorag
 
     @Override
     public void destroy() {
+        // Drop any references to any current requests.
+        mCurrentRequest = null;
+        mRequestQueue.clear();
+
         ThreadUtils.assertOnUiThread();
         mStorage.destroy();
         mBitmapCache.destroy();
@@ -195,6 +199,9 @@ public class ThumbnailProviderImpl implements ThumbnailProvider, ThumbnailStorag
      */
     @Override
     public void onThumbnailRetrieved(@NonNull String contentId, @Nullable Bitmap bitmap) {
+        // Early-out if we have no actual current request.
+        if (mCurrentRequest == null) return;
+
         if (bitmap != null) {
             // The bitmap returned here is retrieved from the native side. The image decoder there
             // scales down the image (if it is too big) so that one of its sides is smaller than or