mus: Use TooltipManagerAura in NativeWidgetMus.

ui/views/mus/window_manager_connection.cc

Index: ui/views/mus/window_manager_connection.cc
diff --git a/ui/views/mus/window_manager_connection.cc b/ui/views/mus/window_manager_connection.cc
index 8c4cf85d690d545d2fa9dd9e3da5723597200e45..e435d9451f765d30f2ea5491c0c64554b20f5f91 100644
--- a/ui/views/mus/window_manager_connection.cc
+++ b/ui/views/mus/window_manager_connection.cc
@@ -4,6 +4,7 @@
 
 #include "ui/views/mus/window_manager_connection.h"
 
+#include <algorithm>
 #include <set>
 #include <utility>
 
@@ -39,6 +40,34 @@ using WindowManagerConnectionPtr =
 base::LazyInstance<WindowManagerConnectionPtr>::Leaky lazy_tls_ptr =
     LAZY_INSTANCE_INITIALIZER;
 
+ui::Window* GetWindowFrom(const std::vector<display::Display>& displays,
+                          const std::vector<ui::Window*>& windows,
+                          const gfx::Point& screen_point) {
+  for (ui::Window* window : windows) {
+    const int64_t window_display_id = window->GetRoot()->display_id();

[sky, 2016/10/06 21:23:42]

Each window has a display id, so you should be able to use window->display_id()
here.

+    for (display::Display display : displays) {

[sky, 2016/10/06 21:23:42]

As you're going to be doing this in a loop every time I think it's worth
building a map display_id to display that you pass to this function.

+      if (display.id() != window_display_id)
+        continue;
+
+      gfx::Point display_origin = display.bounds().origin();
+      gfx::Rect bounds_in_screen = window->GetBoundsInRoot();
+      bounds_in_screen.Offset(display_origin.x(), display_origin.y());
+
+      if (bounds_in_screen.Contains(screen_point)) {
+        if (!window->children().empty()) {
+          ui::Window* child =
+              GetWindowFrom(displays, window->children(), screen_point);
+          if (child)
+            return child;
+        }
+
+        return window;
+      }
+    }
+  }
+  return nullptr;
+}
+
 }  // namespace
 
 WindowManagerConnection::~WindowManagerConnection() {
@@ -167,6 +196,17 @@ gfx::Point WindowManagerConnection::GetCursorScreenPoint() {
   return client_->GetCursorScreenPoint();
 }
 
+ui::Window* WindowManagerConnection::GetWindowAtScreenPoint(

[sky, 2016/10/06 21:23:42]

Please add test coverage of this.

+    const gfx::Point& point) {
+  std::vector<display::Display> displays =
+      display::Screen::GetScreen()->GetAllDisplays();
+
+  const std::set<ui::Window*>& roots = GetRoots();
+  std::vector<ui::Window*> windows;
+  std::copy(roots.begin(), roots.end(), std::back_inserter(windows));
+  return GetWindowFrom(displays, windows, point);
+}
+
 std::unique_ptr<OSExchangeData::Provider>
 WindowManagerConnection::BuildProvider() {
   return base::MakeUnique<OSExchangeDataProviderMus>();