add ability to get FBO ID to Surface

BUG=skia:

Review URL: https://codereview.chromium.org/1220733007
diff --git a/src/image/SkSurface.cpp b/src/image/SkSurface.cpp
index 35409be..2e8c7fa 100644
--- a/src/image/SkSurface.cpp
+++ b/src/image/SkSurface.cpp
@@ -175,10 +175,14 @@
     return this->getCanvas()->readPixels(dstInfo, dstPixels, dstRowBytes, srcX, srcY);
 }
 
-GrBackendObject SkSurface::getTextureHandle(TextureHandleAccess access) {
+GrBackendObject SkSurface::getTextureHandle(BackendHandleAccess access) {
     return asSB(this)->onGetTextureHandle(access);
 }
 
+bool SkSurface::getRenderTargetHandle(GrBackendObject* obj, BackendHandleAccess access) {
+    return asSB(this)->onGetRenderTargetHandle(obj, access);
+}
+
 //////////////////////////////////////////////////////////////////////////////////////
 
 #if !SK_SUPPORT_GPU