Discard atlas after every MultiPictureDraw::draw

src/gpu/GrLayerHoister.h

Index: src/gpu/GrLayerHoister.h
diff --git a/src/gpu/GrLayerHoister.h b/src/gpu/GrLayerHoister.h
index 82dd967bb3c32ace572a5dfd366acef4746c3270..c3a451df572583fcb8db4d60c4b9a1b77dd2c62f 100644
--- a/src/gpu/GrLayerHoister.h
+++ b/src/gpu/GrLayerHoister.h
@@ -87,6 +87,12 @@ public:
         @param layers     Unneeded layers in the atlas
     */
     static void UnlockLayers(GrContext* context, const SkTDArray<GrHoistedLayer>& layers);
+
+    /** Forceably remove all cached layers and release the atlas. Useful for debugging and timing.
+        This is only functional when GR_CACHE_HOISTED_LAYERS is set to 1 in GrLayerCache.h
+        @param context    Owner of the layer cache (and thus the layers)
+     */
+    static void PurgeCache(GrContext* context);
 };
 
 #endif