add ability to get FBO ID to Surface

src/gpu/gl/GrGLRenderTarget.h

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #ifndef GrGLRenderTarget_DEFINED
 #define GrGLRenderTarget_DEFINED
@@ skipping 37 matching lines @@
             fRTFBOID == fTexFBOID) {
             // catches FBO 0 and non MSAA case
             return kAutoResolves_ResolveType;
         } else if (kUnresolvableFBOID == fTexFBOID) {
             return kCantResolve_ResolveType;
         } else {
             return kCanResolve_ResolveType;
         }
     }
 
+    GrBackendObject getRenderTargetHandle() const override { return fRTFBOID; }
+
     /** When we don't own the FBO ID we don't attempt to modify its attachments. */
     bool canAttemptStencilAttachment() const override {
         return kCached_LifeCycle == fRTLifecycle || kUncached_LifeCycle == fRTLifecycle;
     }
 
 protected:
     // The public constructor registers this object with the cache. However, only the most derived
     // class should register with the cache. This constructor does not do the registration and
     // rather moves that burden onto the derived class.
     enum Derived { kDerived };
@@ skipping 22 matching lines @@
     GrGLIRect   fViewport;
 
     // onGpuMemorySize() needs to know the VRAM footprint of the FBO(s). However, abandon and
     // release zero out the IDs and the cache needs to know the size even after those actions.
     size_t      fGpuMemorySize;
 
     typedef GrRenderTarget INHERITED;
 };
 
 #endif