add ability to get FBO ID to Surface

BUG=skia:

Review URL: https://codereview.chromium.org/1220733007
diff --git a/src/image/SkSurface_Gpu.h b/src/image/SkSurface_Gpu.h
index ed94a24..2324154 100644
--- a/src/image/SkSurface_Gpu.h
+++ b/src/image/SkSurface_Gpu.h
@@ -16,12 +16,11 @@
 
 class SkSurface_Gpu : public SkSurface_Base {
 public:
-    
-
     SkSurface_Gpu(SkGpuDevice*);
     virtual ~SkSurface_Gpu();
 
-    GrBackendObject onGetTextureHandle(TextureHandleAccess) override;
+    GrBackendObject onGetTextureHandle(BackendHandleAccess) override;
+    bool onGetRenderTargetHandle(GrBackendObject*, BackendHandleAccess) override;
     SkCanvas* onNewCanvas() override;
     SkSurface* onNewSurface(const SkImageInfo&) override;
     SkImage* onNewImageSnapshot(Budgeted) override;