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

ui/gl/gl_image_io_surface.cc

Index: ui/gl/gl_image_io_surface.cc
diff --git a/ui/gl/gl_image_io_surface.cc b/ui/gl/gl_image_io_surface.cc
index 9d27a290d32a7bc2597a8d25247ef87fe470b450..2bb328bb0e6d11f4d948c4babb1117579275b790 100644
--- a/ui/gl/gl_image_io_surface.cc
+++ b/ui/gl/gl_image_io_surface.cc
@@ -16,22 +16,26 @@ GLImageIOSurface::GLImageIOSurface(const gfx::Size& size) : size_(size) {
 }
 
 GLImageIOSurface::~GLImageIOSurface() {
+  DCHECK(thread_checker_.CalledOnValidThread());
   DCHECK(!io_surface_);
 }
 
 bool GLImageIOSurface::Initialize(IOSurfaceRef io_surface) {
+  DCHECK(thread_checker_.CalledOnValidThread());
   DCHECK(!io_surface_);
   io_surface_.reset(io_surface);
   return true;
 }
 
 void GLImageIOSurface::Destroy(bool have_context) {
+  DCHECK(thread_checker_.CalledOnValidThread());
   io_surface_.reset();
 }
 
 gfx::Size GLImageIOSurface::GetSize() { return size_; }
 
 bool GLImageIOSurface::BindTexImage(unsigned target) {
+  DCHECK(thread_checker_.CalledOnValidThread());
   if (target != GL_TEXTURE_RECTANGLE_ARB) {
     // This might be supported in the future. For now, perform strict
     // validation so we know what's going on.