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/src/gpu/GrContext.cpp b/src/gpu/GrContext.cpp
index 2132ed6..975f6d0 100644
--- a/src/gpu/GrContext.cpp
+++ b/src/gpu/GrContext.cpp
@@ -115,6 +115,10 @@
     GrSafeSetNull(fPathRendererChain);
 }
 
+size_t GrContext::getGpuTextureCacheBytes() const {
+  return fTextureCache->getCachedResourceBytes();
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 
 int GrContext::PaintStageVertexLayoutBits(