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

chrome/browser/android/vr_shell/vr_compositor.cc

Index: chrome/browser/android/vr_shell/vr_compositor.cc
diff --git a/chrome/browser/android/vr_shell/vr_compositor.cc b/chrome/browser/android/vr_shell/vr_compositor.cc
index 9d5d05e29802743fde8a8dc4b41f32b615bbaa6f..882236f53d8c54bc360732be0577f7ce87a000b4 100644
--- a/chrome/browser/android/vr_shell/vr_compositor.cc
+++ b/chrome/browser/android/vr_shell/vr_compositor.cc
@@ -54,8 +54,9 @@ void VrCompositor::SurfaceDestroyed() {
   compositor_->SetSurface(nullptr);
 }
 
-void VrCompositor::SetWindowBounds(int width, int height) {
-  compositor_->SetWindowBounds(gfx::Size(width, height));
+void VrCompositor::SetWindowBounds(gfx::Size size) {
+  bounds_ = size;
+  compositor_->SetWindowBounds(bounds_);
 }
 
 void VrCompositor::SurfaceChanged(jobject surface) {