Photo Picker dialog: Add UMA statistics.

chrome/android/java/src/org/chromium/chrome/browser/photo_picker/PickerAdapter.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.support.annotation.IntDef;
 import android.support.v7.widget.RecyclerView.Adapter;
 import android.support.v7.widget.RecyclerView.ViewHolder;
 import android.view.LayoutInflater;
 import android.view.View;
 import android.view.ViewGroup;
 
 import org.chromium.chrome.R;
 
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+
 /**
  * A data adapter for the Photo Picker.
  */
 public class PickerAdapter extends Adapter<ViewHolder> {
+    // The possible types of actions required during decoding.
+    @IntDef({NO_ACTION, FROM_CACHE, DECODE})
+    @Retention(RetentionPolicy.SOURCE)
+    public @interface DecodeActions {}
+    public static final int NO_ACTION = 0; // Gallery/Camera tile: No action.
+    public static final int FROM_CACHE = 1; // Image already decoded.
+    public static final int DECODE = 2; // Image needed to be decoded.
+
     // The category view to use to show the images.
     private PickerCategoryView mCategoryView;
 
+    // How many times the (high-res) cache was useful.
+    @DecodeActions
+    private int mCacheHits;
+
+    // How many times a decoding was requested.
+    @DecodeActions
+    private int mDecodeRequests;
+
     /**
      * The PickerAdapter constructor.
      * @param categoryView The category view to use to show the images.
      */
     public PickerAdapter(PickerCategoryView categoryView) {
         mCategoryView = categoryView;
     }
 
     // RecyclerView.Adapter:
 
     @Override
     public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
         View itemView = LayoutInflater.from(parent.getContext())
                                 .inflate(R.layout.photo_picker_bitmap_view, parent, false);
         PickerBitmapView bitmapView = (PickerBitmapView) itemView;
         bitmapView.setCategoryView(mCategoryView);
         return new PickerBitmapViewHolder(bitmapView);
     }
 
     @Override
     public void onBindViewHolder(ViewHolder holder, int position) {
         if (holder instanceof PickerBitmapViewHolder) {
             PickerBitmapViewHolder myHolder = (PickerBitmapViewHolder) holder;
-            myHolder.displayItem(mCategoryView, position);
+            int result = myHolder.displayItem(mCategoryView, position);
+            if (result == FROM_CACHE) {
+                mCacheHits++;
+            } else if (result == DECODE) {
+                mDecodeRequests++;
+            }
         }
     }
 
     @Override
     public int getItemCount() {
         return mCategoryView.getPickerBitmaps().size();
     }
+
+    /** Returns the number of times the cache supplied a bitmap. */
+    public int getCacheHitCount() {
+        return mCacheHits;
+    }
+
+    /** Returns the number of decode requests (cache-misses). */
+    public int getDecodeRequestCount() {
+        return mDecodeRequests;
+    }
 }