Fix offscreen rendering on iOS by not assuming that the default window bound framebuffer is 0

sky/shell/gpu/ganesh_surface.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef SKY_SHELL_GPU_GANESH_SURFACE_H_
 #define SKY_SHELL_GPU_GANESH_SURFACE_H_
 
 #include "base/memory/scoped_ptr.h"
 #include "skia/ext/refptr.h"
 #include "sky/shell/gpu/ganesh_context.h"
 #include "third_party/skia/include/core/SkSurface.h"
 #include "ui/gfx/geometry/size.h"
 
 namespace sky {
 namespace shell {
 
 // GaneshSurface holds an SkSurface configured to render with Ganesh. Using the
-// provided GaneshContext, GaneshSurface wraps an SkSurface around FBO 0 so that
-// you can use |canvas()| to draw to FBO 0.
+// provided GaneshContext, GaneshSurface wraps an SkSurface around the window
+// bound FBO so that you can use |canvas()| to draw to that window bound FBO.
 class GaneshSurface {
  public:
-  GaneshSurface(GaneshContext* context, const gfx::Size& size);
+  GaneshSurface(intptr_t window_fbo,
+                GaneshContext* context,
+                const gfx::Size& size);
   ~GaneshSurface();
 
   SkCanvas* canvas() const { return surface_->getCanvas(); }
   gfx::Size size() const {
     return gfx::Size(surface_->width(), surface_->height());
   }
 
  private:
   skia::RefPtr<SkSurface> surface_;
 
   DISALLOW_COPY_AND_ASSIGN(GaneshSurface);
 };
 
 }  // namespace shell
 }  // namespace sky
 
 #endif  // SKY_SHELL_GPU_GANESH_SURFACE_H_