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 70d18a837fd8316262c9c3918ccda1a786811a35..ad2d23235185cb46e1b793e91f533fb33886f077 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
@@ -45,6 +45,16 @@ public class PickerBitmapViewHolder extends ViewHolder {
             return;
         }
 
+        if (mCategoryView.getHighResBitmaps().get(filePath) == null) {
+            mCategoryView.getHighResBitmaps().put(filePath, bitmap);

[Michael van Ouwerkerk, 2017/04/27 17:07:34]

The documentation for this param says it might be a placeholder image on
failure. Should that be stored in the cache?

[Finnur, 2017/05/04 16:05:15]

That changed with the latest sync. Decoding will not return a placeholder image
on failure any longer (just a null bitmap).

+        }
+
+        if (mCategoryView.getLowResBitmaps().get(filePath) == null) {
+            // Scaling the image down takes between 0-1 ms on average (Nexus 6 phone debug build).
+            Bitmap lowres = BitmapUtils.scale(bitmap, 40, false);

[Michael van Ouwerkerk, 2017/04/27 17:07:34]

What's 40? Px? Dp? Maybe extract a documented constant.

[Finnur, 2017/05/04 16:05:15]

Done.

+            mCategoryView.getLowResBitmaps().put(filePath, lowres);
+        }
+
         if (!TextUtils.equals(mBitmapDetails.getFilePath(), filePath)) {
             return;
         }
@@ -69,10 +79,24 @@ public class PickerBitmapViewHolder extends ViewHolder {
             return;
         }
 
-        // TODO(finnur): Use cached image, if available.
+        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);
+        }
 
         // TODO(finnur): Use decoder instead.
-        int size = mCategoryView.getImageSize();
         imageDecodedCallback(mBitmapDetails.getFilePath(), createPlaceholderBitmap(size, size));
     }