Set capture to the window being dragged when dragging a window on Ash

ash/wm/toplevel_window_event_handler.cc

Index: ash/wm/toplevel_window_event_handler.cc
diff --git a/ash/wm/toplevel_window_event_handler.cc b/ash/wm/toplevel_window_event_handler.cc
index 610261f9f78b21a0c2fce52c4091a2e9ace5232d..cc0362e0ece038b331aca7a1aba5289937ffb18d 100644
--- a/ash/wm/toplevel_window_event_handler.cc
+++ b/ash/wm/toplevel_window_event_handler.cc
@@ -110,6 +110,9 @@ class ToplevelWindowEventHandler::ScopedWindowResizer
   ToplevelWindowEventHandler* handler_;
   scoped_ptr<WindowResizer> resizer_;
 
+  // Whether ScopedWindowResizer grabbed capture.
+  bool grabbed_capture_;
+
   DISALLOW_COPY_AND_ASSIGN(ScopedWindowResizer);
 };
 
@@ -117,14 +120,24 @@ ToplevelWindowEventHandler::ScopedWindowResizer::ScopedWindowResizer(
     ToplevelWindowEventHandler* handler,
     WindowResizer* resizer)
     : handler_(handler),
-      resizer_(resizer) {
-  resizer_->GetTarget()->AddObserver(this);
-  wm::GetWindowState(resizer_->GetTarget())->AddObserver(this);
+      resizer_(resizer),
+      grabbed_capture_(false) {
+  aura::Window* target = resizer_->GetTarget();
+  target->AddObserver(this);
+  wm::GetWindowState(target)->AddObserver(this);
+
+  if (!target->HasCapture()) {
+    grabbed_capture_ = true;
+    target->SetCapture();
+  }
 }
 
 ToplevelWindowEventHandler::ScopedWindowResizer::~ScopedWindowResizer() {
-  resizer_->GetTarget()->RemoveObserver(this);
-  wm::GetWindowState(resizer_->GetTarget())->RemoveObserver(this);
+  aura::Window* target = resizer_->GetTarget();
+  target->RemoveObserver(this);
+  wm::GetWindowState(target)->RemoveObserver(this);
+  if (grabbed_capture_)
+    target->ReleaseCapture();
 }
 
 bool ToplevelWindowEventHandler::ScopedWindowResizer::IsMove() const {