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

ui/gl/gl_image_egl.cc

 // Copyright (c) 2013 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_egl.h"
 
 #include "ui/gl/egl_util.h"
 #include "ui/gl/gl_surface_egl.h"
 
 namespace gfx {
 
 GLImageEGL::GLImageEGL(const gfx::Size& size)
     : egl_image_(EGL_NO_IMAGE_KHR), size_(size) {
 }
 
 GLImageEGL::~GLImageEGL() {
+  DCHECK(thread_checker_.CalledOnValidThread());
   DCHECK_EQ(EGL_NO_IMAGE_KHR, egl_image_);
 }
 
 bool GLImageEGL::Initialize(EGLenum target,
                             EGLClientBuffer buffer,
                             const EGLint* attrs) {
+  DCHECK(thread_checker_.CalledOnValidThread());
   DCHECK_EQ(EGL_NO_IMAGE_KHR, egl_image_);
   egl_image_ = eglCreateImageKHR(GLSurfaceEGL::GetHardwareDisplay(),
                                  EGL_NO_CONTEXT,
                                  target,
                                  buffer,
                                  attrs);
   if (egl_image_ == EGL_NO_IMAGE_KHR) {
     DLOG(ERROR) << "Error creating EGLImage: " << ui::GetLastEGLErrorString();
     return false;
   }
 
   return true;
 }
 
 void GLImageEGL::Destroy(bool have_context) {
+  DCHECK(thread_checker_.CalledOnValidThread());
   if (egl_image_ != EGL_NO_IMAGE_KHR) {
     EGLBoolean result =
         eglDestroyImageKHR(GLSurfaceEGL::GetHardwareDisplay(), egl_image_);
     if (result == EGL_FALSE) {
       DLOG(ERROR) << "Error destroying EGLImage: "
                   << ui::GetLastEGLErrorString();
     }
     egl_image_ = EGL_NO_IMAGE_KHR;
   }
 }
 
 gfx::Size GLImageEGL::GetSize() { return size_; }
 
 bool GLImageEGL::BindTexImage(unsigned target) {
+  DCHECK(thread_checker_.CalledOnValidThread());
   DCHECK_NE(EGL_NO_IMAGE_KHR, egl_image_);
   glEGLImageTargetTexture2DOES(target, egl_image_);
   DCHECK_EQ(static_cast<GLenum>(GL_NO_ERROR), glGetError());
   return true;
 }
 
 bool GLImageEGL::CopyTexImage(unsigned target) {
   return false;
 }
 
 bool GLImageEGL::ScheduleOverlayPlane(gfx::AcceleratedWidget widget,
                                       int z_order,
                                       OverlayTransform transform,
                                       const Rect& bounds_rect,
                                       const RectF& crop_rect) {
   return false;
 }
 
 }  // namespace gfx