Fix some thread safety violations in device::GvrDelegate implementation.

chrome/browser/android/vr_shell/vr_compositor.h

Index: chrome/browser/android/vr_shell/vr_compositor.h
diff --git a/chrome/browser/android/vr_shell/vr_compositor.h b/chrome/browser/android/vr_shell/vr_compositor.h
index a9c559a843b9f23f7da840fb20af006dad6192ce..a0e872029c7484871c01c28b90763d5adba8e413 100644
--- a/chrome/browser/android/vr_shell/vr_compositor.h
+++ b/chrome/browser/android/vr_shell/vr_compositor.h
@@ -10,6 +10,7 @@
 #include "base/android/scoped_java_ref.h"
 #include "base/macros.h"
 #include "content/public/browser/android/compositor_client.h"
+#include "ui/gfx/geometry/size.h"
 
 typedef unsigned int SkColor;
 
@@ -34,7 +35,8 @@ class VrCompositor : public content::CompositorClient {
   ~VrCompositor() override;
 
   void SurfaceDestroyed();
-  void SetWindowBounds(int width, int height);
+  void SetWindowBounds(gfx::Size size);
+  gfx::Size GetWindowBounds() { return bounds_; }
   void SurfaceChanged(jobject surface);
   void SetLayer(content::WebContents* web_contents);
 
@@ -44,6 +46,7 @@ class VrCompositor : public content::CompositorClient {
 
  private:
   std::unique_ptr<content::Compositor> compositor_;
+  gfx::Size bounds_;
 
   cc::Layer* layer_ = nullptr;
   cc::Layer* layer_parent_ = nullptr;