Have GrSurfaceProxys and GrGpuResources draw from the same pool of unique ids

src/gpu/GrSurfaceProxy.cpp

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrSurfaceProxy.h"
 
-#include "SkAtomics.h"
-
-uint32_t GrSurfaceProxy::CreateUniqueID() {
-    static int32_t gUniqueID = SK_InvalidUniqueID;
-    uint32_t id;
-    do {
-        id = static_cast<uint32_t>(sk_atomic_inc(&gUniqueID) + 1);
-    } while (id == SK_InvalidUniqueID);
-    return id;
-}