Update bench pictures to time image decode & upload costs

include/gpu/GrContext.h

Index: include/gpu/GrContext.h
===================================================================
--- include/gpu/GrContext.h	(revision 12709)
+++ include/gpu/GrContext.h	(working copy)
@@ -210,6 +210,13 @@
     void purgeCache();
 
     /**
+     * Purge all the unlocked resources from the cache.
+     * This entry point is mainly meant for timing texture uploads
+     * and is only available if defined outside of Skia (see bench_pictures).

[bsalomon, 2013/12/18 16:16:12]

maybe instead of "is only available if defined outside of Skia", "is not defined
in normal builds of Skia" 

It's not like we want to encourage clients to provide alternate definitions :)

+     */
+    void purgeAllUnlockedResources();
+
+    /**
      * Creates a texture that is outside the cache. Does not count against
      * cache's budget.
      */