Introduce XGetImage() for GrabWindowSnapshot() in ChromeOS.

ui/aura/root_window_host_win.cc

Index: ui/aura/root_window_host_win.cc
diff --git a/ui/aura/root_window_host_win.cc b/ui/aura/root_window_host_win.cc
index 79060c0ecd49af39df5412b180193701a99fd0d8..d2167d71d47aeb993b1d78f8c651c29b209ba98c 100644
--- a/ui/aura/root_window_host_win.cc
+++ b/ui/aura/root_window_host_win.cc
@@ -267,6 +267,13 @@ bool RootWindowHostWin::ConfineCursorToRootWindow() {
   return ClipCursor(&window_rect) != 0;
 }
 
+bool RootWindowHostWin::GrabSnapshot(
+    const gfx::Rect& snapshot_bounds,
+    std::vector<unsigned char>* png_representation) {
+  NOTIMPLEMENTED();
+  return false;
+}
+
 void RootWindowHostWin::UnConfineCursor() {
   ClipCursor(NULL);
 }