patch from issue 886233004 at patchset 40001 (http://crrev.com/886233004#ps40001)

... with changes proposed in the review.

BUG=skia:

Review URL: https://codereview.chromium.org/894013002
diff --git a/dm/DMGpuSupport.h b/dm/DMGpuSupport.h
index 032151f..1ced019 100644
--- a/dm/DMGpuSupport.h
+++ b/dm/DMGpuSupport.h
@@ -42,6 +42,12 @@
 };
 static const int kGrGLStandardCnt = 3;
 
+class GrContext {
+public:
+    void dumpCacheStats(SkString*) const {}
+    void dumpGpuStats(SkString*) const {}
+};
+
 class GrContextFactory {
 public:
     typedef int GLContextType;