Introduce XGetImage() for GrabWindowSnapshot() in ChromeOS.

ui/aura/root_window.cc

Index: ui/aura/root_window.cc
diff --git a/ui/aura/root_window.cc b/ui/aura/root_window.cc
index 48a202e97188b8275a0270bdff8d2093123c916f..066e5146b046a4ad2b526e30ff07df37e2ae331b 100644
--- a/ui/aura/root_window.cc
+++ b/ui/aura/root_window.cc
@@ -548,6 +548,13 @@ void RootWindow::SetFocusWhenShown(bool focused) {
   host_->SetFocusWhenShown(focused);
 }
 
+bool RootWindow::GrabWindowSnapshot(
+    std::vector<unsigned char>* png_representation,
+    const gfx::Rect& snapshot_bounds) {
+  DCHECK(bounds().Contains(snapshot_bounds));
+  return host_->GrabWindowSnapshot(png_representation, snapshot_bounds);
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // RootWindow, Window overrides: