mash: make Env::last_mouse_location() accurate for Mus

ui/aura/env.cc

Index: ui/aura/env.cc
diff --git a/ui/aura/env.cc b/ui/aura/env.cc
index 5e9411332e3aacd7299bd6c5c1a08fc6c58e8fce..9704b641579870d56bd2f201f6d192f8dca63a7f 100644
--- a/ui/aura/env.cc
+++ b/ui/aura/env.cc
@@ -123,6 +123,15 @@ bool Env::IsMouseButtonDown() const {
       mouse_button_flags_ != 0;
 }
 
+const gfx::Point& Env::last_mouse_location() {
+  if (mode_ == Mode::LOCAL || !get_last_mouse_location_from_mus_)
+    return last_mouse_location_;
+
+  DCHECK(window_tree_client_);
+  last_mouse_location_ = window_tree_client_->GetCursorScreenPoint();
+  return last_mouse_location_;
+}
+
 void Env::SetWindowTreeClient(WindowTreeClient* window_tree_client) {
   // The WindowTreeClient should only be set once. Test code may need to change
   // the value after the fact, to do that use EnvTestHelper.
@@ -155,6 +164,7 @@ Env::Env(Mode mode)
     : mode_(mode),
       mouse_button_flags_(0),
       is_touch_down_(false),
+      get_last_mouse_location_from_mus_(mode_ == Mode::MUS),
       input_state_lookup_(InputStateLookup::Create()),
       context_factory_(nullptr),
       context_factory_private_(nullptr) {