Introdcue AshWindowTreeHost and move ash/chrome specific code in WTH to ash.

ui/aura/remote_window_tree_host_win.cc

Index: ui/aura/remote_window_tree_host_win.cc
diff --git a/ui/aura/remote_window_tree_host_win.cc b/ui/aura/remote_window_tree_host_win.cc
index 19715ba4f3ff8e9aab10a125270a42b7a9d1405d..6525588cfee9dab063f276aba79b894ff4d98de5 100644
--- a/ui/aura/remote_window_tree_host_win.cc
+++ b/ui/aura/remote_window_tree_host_win.cc
@@ -149,16 +149,17 @@ void HandleMetroExit() {
 
 RemoteWindowTreeHostWin* g_instance = NULL;
 
+// static
 RemoteWindowTreeHostWin* RemoteWindowTreeHostWin::Instance() {
-  if (g_instance)
-    return g_instance;
-  return Create(gfx::Rect());
+  if (!g_instance)
+    g_instance = new RemoteWindowTreeHostWin(gfx::Rect());
+  return g_instance;
 }
 
-RemoteWindowTreeHostWin* RemoteWindowTreeHostWin::Create(
-    const gfx::Rect& bounds) {
-  g_instance = g_instance ? g_instance : new RemoteWindowTreeHostWin(bounds);
-  return g_instance;
+// static
+void RemoteWindowTreeHostWin::SetInstance(RemoteWindowTreeHostWin* instance) {
+  CHECK(!g_instance);
+  g_instance = instance;
 }
 
 RemoteWindowTreeHostWin::RemoteWindowTreeHostWin(const gfx::Rect& bounds)
@@ -390,9 +391,6 @@ void RemoteWindowTreeHostWin::Hide() {
   NOTIMPLEMENTED();
 }
 
-void RemoteWindowTreeHostWin::ToggleFullScreen() {
-}
-
 gfx::Rect RemoteWindowTreeHostWin::GetBounds() const {
   return gfx::Rect(window_size_);
 }
@@ -402,13 +400,6 @@ void RemoteWindowTreeHostWin::SetBounds(const gfx::Rect& bounds) {
   OnHostResized(bounds.size());
 }
 
-gfx::Insets RemoteWindowTreeHostWin::GetInsets() const {
-  return gfx::Insets();
-}
-
-void RemoteWindowTreeHostWin::SetInsets(const gfx::Insets& insets) {
-}
-
 gfx::Point RemoteWindowTreeHostWin::GetLocationOnNativeScreen() const {
   return gfx::Point(0, 0);
 }
@@ -433,13 +424,6 @@ bool RemoteWindowTreeHostWin::QueryMouseLocation(gfx::Point* location_return) {
   return true;
 }
 
-bool RemoteWindowTreeHostWin::ConfineCursorToRootWindow() {
-  return true;
-}
-
-void RemoteWindowTreeHostWin::UnConfineCursor() {
-}
-
 void RemoteWindowTreeHostWin::SetCursorNative(gfx::NativeCursor native_cursor) {
   if (!host_)
     return;