update skpdiff visualization (image magnification with alpha mask)

R=epoger@google.com

Review URL: https://codereview.chromium.org/29103005

git-svn-id: http://skia.googlecode.com/svn/trunk@12174 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/tools/skpdiff/SkDifferentPixelsMetric.h b/tools/skpdiff/SkDifferentPixelsMetric.h
index 38fa5ac..614f920 100644
--- a/tools/skpdiff/SkDifferentPixelsMetric.h
+++ b/tools/skpdiff/SkDifferentPixelsMetric.h
@@ -27,13 +27,17 @@
     public SkImageDiffer {
 #endif
 public:
+    SkDifferentPixelsMetric() : fPOIAlphaMask(false) {}
+
     virtual const char* getName() SK_OVERRIDE;
+    virtual bool enablePOIAlphaMask() SK_OVERRIDE;
     virtual int queueDiff(SkBitmap* baseline, SkBitmap* test) SK_OVERRIDE;
     virtual void deleteDiff(int id) SK_OVERRIDE;
     virtual bool isFinished(int id) SK_OVERRIDE;
     virtual double getResult(int id) SK_OVERRIDE;
     virtual int getPointsOfInterestCount(int id) SK_OVERRIDE;
     virtual SkIPoint* getPointsOfInterest(int id) SK_OVERRIDE;
+    virtual SkBitmap* getPointsOfInterestAlphaMask(int id) SK_OVERRIDE;
 
 protected:
 #if SK_SUPPORT_OPENCL
@@ -41,8 +45,9 @@
 #endif
 
 private:
-    struct QueuedDiff;
+    bool fPOIAlphaMask;
 
+    struct QueuedDiff;
     SkTDArray<QueuedDiff> fQueuedDiffs;
 
 #if SK_SUPPORT_OPENCL