Expose functionality to purge the GPU texture cache while running SampleApp.

Press 'p' to purge the cache.  A summary of the number of bytes of video memory
released is output to the command prompt.
Review URL: https://codereview.appspot.com/5587045

git-svn-id: http://skia.googlecode.com/svn/trunk@3097 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/include/gpu/GrContext.h b/include/gpu/GrContext.h
index d27b963..ca440a6 100644
--- a/include/gpu/GrContext.h
+++ b/include/gpu/GrContext.h
@@ -75,6 +75,11 @@
      */
     void freeGpuResources();
 
+    /**
+     * Returns the number of bytes of GPU memory hosted by the texture cache.
+     */
+    size_t getGpuTextureCacheBytes() const;
+
     ///////////////////////////////////////////////////////////////////////////
     // Textures
 
@@ -858,4 +863,3 @@
 };
 
 #endif
-