Photo Picker Dialog: Add caching for the decoded images.

chrome/android/java/src/org/chromium/chrome/browser/photo_picker/PickerBitmapViewHolder.java

 // Copyright 2017 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.
 
 package org.chromium.chrome.browser.photo_picker;
 
+import android.content.res.Resources;
 import android.graphics.Bitmap;
+import android.os.AsyncTask;
 import android.support.v7.widget.RecyclerView.ViewHolder;
 import android.text.TextUtils;
 
+import org.chromium.chrome.R;
+
 import java.util.List;
 
 /**
  * Holds on to a {@link PickerBitmapView} that displays information about a picker bitmap.
  */
 public class PickerBitmapViewHolder
         extends ViewHolder implements DecoderServiceHost.ImageDecodedCallback {
     // Our parent category.
     private PickerCategoryView mCategoryView;
 
@@ skipping 13 matching lines @@
     }
 
     // DecoderServiceHost.ImageDecodedCallback
 
     @Override
     public void imageDecodedCallback(String filePath, Bitmap bitmap) {
         if (bitmap == null || bitmap.getWidth() == 0 || bitmap.getHeight() == 0) {
             return;
         }
 
+        if (mCategoryView.getHighResBitmaps().get(filePath) == null) {
+            mCategoryView.getHighResBitmaps().put(filePath, bitmap);
+        }
+
+        if (mCategoryView.getLowResBitmaps().get(filePath) == null) {
+            Resources resources = mItemView.getContext().getResources();
+            new BitmapScalerTask(mCategoryView.getLowResBitmaps(), filePath,
+                    resources.getDimensionPixelSize(R.dimen.photo_picker_grainy_thumbnail_size))
+                    .executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR, bitmap);
+        }
+
         if (!TextUtils.equals(mBitmapDetails.getFilePath(), filePath)) {
             return;
         }
 
         if (mItemView.setThumbnailBitmap(bitmap)) {
             mItemView.fadeInThumbnail();
         }
     }
 
     /**
      * Display a single item from |position| in the PickerCategoryView.
      * @param categoryView The PickerCategoryView to use to fetch the image.
      * @param position The position of the item to fetch.
      */
     public void displayItem(PickerCategoryView categoryView, int position) {
         mCategoryView = categoryView;
 
         List<PickerBitmap> pickerBitmaps = mCategoryView.getPickerBitmaps();
         mBitmapDetails = pickerBitmaps.get(position);
 
         if (mBitmapDetails.type() == PickerBitmap.CAMERA
                 || mBitmapDetails.type() == PickerBitmap.GALLERY) {
             mItemView.initialize(mBitmapDetails, null, false);
             return;
         }
 
-        // TODO(finnur): Use cached image, if available.
-
-        mItemView.initialize(mBitmapDetails, null, true);
+        String filePath = mBitmapDetails.getFilePath();
+        Bitmap original = mCategoryView.getHighResBitmaps().get(filePath);
+        if (original != null) {
+            mItemView.initialize(mBitmapDetails, original, false);
+            return;
+        }
 
         int size = mCategoryView.getImageSize();
-        mCategoryView.getDecoderServiceHost().decodeImage(mBitmapDetails.getFilePath(), size, this);
+        Bitmap placeholder = mCategoryView.getLowResBitmaps().get(filePath);
+        if (placeholder != null) {
+            // For performance stats see http://crbug.com/719919.
+            placeholder = BitmapUtils.scale(placeholder, size, false);
+            mItemView.initialize(mBitmapDetails, placeholder, true);
+        } else {
+            mItemView.initialize(mBitmapDetails, null, true);
+        }
+
+        mCategoryView.getDecoderServiceHost().decodeImage(filePath, size, this);
     }
 
     /**
      * Returns the file path of the current request.
      */
     public String getFilePath() {
         return mBitmapDetails == null ? null : mBitmapDetails.getFilePath();
     }
 }