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

sky/shell/gpu/rasterizer.cc

 // 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.
 
 #include "sky/shell/gpu/rasterizer.h"
 
 #include "base/trace_event/trace_event.h"
 #include "sky/shell/gpu/ganesh_context.h"
 #include "sky/shell/gpu/ganesh_surface.h"
 #include "third_party/skia/include/core/SkCanvas.h"
@@ skipping 36 matching lines @@
 
   if (!surface_)
     return;
 
   gfx::Size size = GetSize(picture.get());
   if (size.IsEmpty())
     return;
 
   EnsureGLContext();
   CHECK(context_->MakeCurrent(surface_.get()));
-  EnsureGaneshSurface(size);
+  EnsureGaneshSurface(surface_->GetBackingFrameBufferObject(), size);
 
   DrawPicture(picture.get());
   surface_->SwapBuffers();
 }
 
 void Rasterizer::DrawPicture(SkPicture* picture) {
   TRACE_EVENT0("sky", "Rasterizer::DrawPicture");
   SkCanvas* canvas = ganesh_surface_->canvas();
   canvas->drawPicture(picture);
   canvas->flush();
 }
 
 void Rasterizer::OnOutputSurfaceDestroyed() {
   ganesh_surface_.reset();
   ganesh_context_.reset();
   context_ = nullptr;
   surface_ = nullptr;
 }
 
 void Rasterizer::EnsureGLContext() {
   if (context_)
     return;
   context_ = gfx::GLContext::CreateGLContext(share_group_.get(), surface_.get(),
                                              gfx::PreferIntegratedGpu);
   CHECK(context_) << "GLContext required.";
   CHECK(context_->MakeCurrent(surface_.get()));
   ganesh_context_.reset(new GaneshContext(context_.get()));
 }
 
-void Rasterizer::EnsureGaneshSurface(const gfx::Size& size) {
+void Rasterizer::EnsureGaneshSurface(intptr_t window_fbo,
+                                     const gfx::Size& size) {
   if (!ganesh_surface_ || ganesh_surface_->size() != size)
-    ganesh_surface_.reset(new GaneshSurface(ganesh_context_.get(), size));
+    ganesh_surface_.reset(
+      new GaneshSurface(window_fbo, ganesh_context_.get(), size));
 }
 
 }  // namespace shell
 }  // namespace sky