Photo Picker Dialog: Add caching for the decoded images.

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

Index: chrome/android/java/src/org/chromium/chrome/browser/photo_picker/PickerBitmapViewHolder.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/photo_picker/PickerBitmapViewHolder.java b/chrome/android/java/src/org/chromium/chrome/browser/photo_picker/PickerBitmapViewHolder.java
index bd8dba0de3b4683aba1e342f1edd57a12cc7ec72..97699c123a320f02c5c3b56a5132b46aea87328f 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/photo_picker/PickerBitmapViewHolder.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/photo_picker/PickerBitmapViewHolder.java
@@ -15,12 +15,18 @@ import java.util.List;
  */
 public class PickerBitmapViewHolder
         extends ViewHolder implements DecoderServiceHost.ImageDecodedCallback {
+    // The size (in dp) of the low-res thumbnails.
+    private static final int GRAINY_THUMBNAIL_SIZE_DP = 12;
+
     // Our parent category.
     private PickerCategoryView mCategoryView;
 
     // The bitmap view we are holding on to.
     private final PickerBitmapView mItemView;
 
+    // The screen density.
+    private final float mDensity;
+
     // The request we are showing the bitmap for.
     private PickerBitmap mBitmapDetails;
 
@@ -31,6 +37,7 @@ public class PickerBitmapViewHolder
     public PickerBitmapViewHolder(PickerBitmapView itemView) {
         super(itemView);
         mItemView = itemView;
+        mDensity = itemView.getContext().getResources().getDisplayMetrics().density;
     }
 
     // DecoderServiceHost.ImageDecodedCallback
@@ -41,6 +48,16 @@ public class PickerBitmapViewHolder
             return;
         }
 
+        if (mCategoryView.getHighResBitmaps().get(filePath) == null) {
+            mCategoryView.getHighResBitmaps().put(filePath, bitmap);
+        }
+
+        if (mCategoryView.getLowResBitmaps().get(filePath) == null) {
+            new BitmapScalerWorkerTask(mCategoryView.getLowResBitmaps(), filePath, bitmap,
+                    (int) (GRAINY_THUMBNAIL_SIZE_DP * mDensity))
+                    .execute();
+        }
+
         if (!TextUtils.equals(mBitmapDetails.getFilePath(), filePath)) {
             return;
         }
@@ -65,11 +82,23 @@ public class PickerBitmapViewHolder
             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();
+        Bitmap placeholder = mCategoryView.getLowResBitmaps().get(filePath);
+        if (placeholder != null) {
+            // Scaling the image up takes between 3-4 ms on average (Nexus 6 phone debug build).
+            placeholder = BitmapUtils.scale(placeholder, size, false);
+            mItemView.initialize(mBitmapDetails, placeholder, true);
+        } else {
+            mItemView.initialize(mBitmapDetails, null, true);
+        }
+
         mCategoryView.getDecoderServiceHost().decodeImage(mBitmapDetails.getFilePath(), size, this);
     }