Fixing leaky handling of SkImage in SkDeferredCanvas.

include/pipe/SkGPipe.h

Index: include/pipe/SkGPipe.h
diff --git a/include/pipe/SkGPipe.h b/include/pipe/SkGPipe.h
index 98e081da5e6b8a306563e56b6deaf70bc34ec1c9..9446b8159f05df933e896a24dafda7509a72e835 100644
--- a/include/pipe/SkGPipe.h
+++ b/include/pipe/SkGPipe.h
@@ -87,6 +87,12 @@ public:
     virtual void notifyWritten(size_t bytes) = 0;
     virtual int numberOfReaders() const { return 1; }
 
+    /**
+     *  Release resource references that are held in internal caches.
+     *  This must only be called after the pipe has been completely flushed.
+     */
+    void purgeCaches();
+
 private:
     friend class SkGPipeWriter;
     void setCanvas(SkGPipeCanvas*);