zero-copy: Clarify to allocate/destroy GpuMemoryBuffer on any thread and use it on the main thread o

ui/gl/gl_image_surface_texture.cc

 // Copyright 2014 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 "ui/gl/gl_image_surface_texture.h"
 
 #include "base/trace_event/trace_event.h"
 #include "ui/gl/android/surface_texture.h"
 
 namespace gfx {
 
 GLImageSurfaceTexture::GLImageSurfaceTexture(const gfx::Size& size)
     : size_(size), texture_id_(0) {
 }
 
 GLImageSurfaceTexture::~GLImageSurfaceTexture() {
+  DCHECK(thread_checker_.CalledOnValidThread());
   DCHECK(!surface_texture_.get());
   DCHECK_EQ(0, texture_id_);
 }
 
 bool GLImageSurfaceTexture::Initialize(SurfaceTexture* surface_texture) {
+  DCHECK(thread_checker_.CalledOnValidThread());
   DCHECK(!surface_texture_.get());
   surface_texture_ = surface_texture;
   return true;
 }
 
 void GLImageSurfaceTexture::Destroy(bool have_context) {
+  DCHECK(thread_checker_.CalledOnValidThread());
   surface_texture_ = NULL;
   texture_id_ = 0;
 }
 
 gfx::Size GLImageSurfaceTexture::GetSize() { return size_; }
 
 bool GLImageSurfaceTexture::BindTexImage(unsigned target) {
   TRACE_EVENT0("gpu", "GLImageSurfaceTexture::BindTexImage");
+  DCHECK(thread_checker_.CalledOnValidThread());
 
   if (target != GL_TEXTURE_EXTERNAL_OES) {
     LOG(ERROR)
         << "Surface texture can only be bound to TEXTURE_EXTERNAL_OES target";
     return false;
   }
 
   GLint texture_id;
   glGetIntegerv(GL_TEXTURE_BINDING_EXTERNAL_OES, &texture_id);
   DCHECK(texture_id);
@@ skipping 32 matching lines @@
 
 bool GLImageSurfaceTexture::ScheduleOverlayPlane(gfx::AcceleratedWidget widget,
                                                  int z_order,
                                                  OverlayTransform transform,
                                                  const Rect& bounds_rect,
                                                  const RectF& crop_rect) {
   return false;
 }
 
 }  // namespace gfx