Add mechanism to proactively purge old resources in GrResourceCache.

src/gpu/GrContext.cpp

Index: src/gpu/GrContext.cpp
diff --git a/src/gpu/GrContext.cpp b/src/gpu/GrContext.cpp
index 4c7f3eabe0e77116974e10160408ed7cb4c94dc8..45f6380e08d2ec7c7673aff2f924223899f69182 100755
--- a/src/gpu/GrContext.cpp
+++ b/src/gpu/GrContext.cpp
@@ -1460,6 +1460,7 @@ void GrContext::flush(int flagsBitfield) {
     } else {
         fDrawBuffer->flush();
     }
+    fResourceCache->notifyFlushOccurred();
     fFlushToReduceCacheSize = false;
 }