fix multithread related crashes in skpdiff

tools/skpdiff/SkDifferentPixelsMetric.h

Index: tools/skpdiff/SkDifferentPixelsMetric.h
diff --git a/tools/skpdiff/SkDifferentPixelsMetric.h b/tools/skpdiff/SkDifferentPixelsMetric.h
index 614f92035672b214ac7b886449fca6742acf4eb3..407ebd02bcfdf0769f0aa81ba09cdceeff4e2575 100644
--- a/tools/skpdiff/SkDifferentPixelsMetric.h
+++ b/tools/skpdiff/SkDifferentPixelsMetric.h
@@ -31,13 +31,7 @@ public:
 
     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;
+    virtual bool diff(SkBitmap* baseline, SkBitmap* test, Result* result) SK_OVERRIDE;
 
 protected:
 #if SK_SUPPORT_OPENCL
@@ -47,9 +41,6 @@ protected:
 private:
     bool fPOIAlphaMask;
 
-    struct QueuedDiff;
-    SkTDArray<QueuedDiff> fQueuedDiffs;
-
 #if SK_SUPPORT_OPENCL
     cl_kernel fKernel;