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

ash/wm/toplevel_window_event_handler.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ash/wm/toplevel_window_event_handler.h"
 
 #include "ash/shell.h"
 #include "ash/wm/resize_shadow_controller.h"
 #include "ash/wm/window_resizer.h"
 #include "ash/wm/window_state.h"
@@ skipping 92 matching lines @@
   void OnWindowDestroying(aura::Window* window) override;
 
   // WindowStateObserver overrides:
   void OnPreWindowStateTypeChange(wm::WindowState* window_state,
                                   wm::WindowStateType type) override;
 
  private:
   ToplevelWindowEventHandler* handler_;
   scoped_ptr<WindowResizer> resizer_;
 
+  // Whether ScopedWindowResizer grabbed capture.
+  bool grabbed_capture_;
+
   DISALLOW_COPY_AND_ASSIGN(ScopedWindowResizer);
 };
 
 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()) {

[flackr, 2014/12/16 21:28:21]

If this is to accomodate X11 already having capture, can we use #if
!defined(USE_X11) instead?

Alternately we could just capture again on X11 assuming it will be a noop.

[pkotwicz, 2014/12/17 04:48:12]

The reason that I do this is because I want to enforce:
"If ScopedWindowResizer grabbed capture, it should release capture."
I think that things are more straightforward this way.

In particular, I want what happens with capture in this scenario to be clear:
- Click on tab
- Drag tab
- Press escape

[flackr, 2014/12/17 19:39:15]

Acknowledged.

+    grabbed_capture_ = true;
+    target->SetCapture();

[flackr, 2014/12/16 21:28:21]

Maybe we should also pay attention to capture loss and stop the drag in such an
event?

[pkotwicz, 2014/12/17 04:48:12]

This would be bad. The tab dragging code switches which aura::Window has capture
prior to ending the drag. See TabDragController::DragBrowserToNewTabStrip()

[pkotwicz, 2014/12/17 05:18:36]

Actually, we already pay attention to loss of capture.
This is why the tab drag is aborted when you use accelerator keys to take a
partial screenshot.

[flackr, 2014/12/17 19:39:15]

Acknowledged, my main concern was losing capture to another application in
windows (or as you mentioned the partial screenshot shortcut). As long as it's
handled looks good.

+  }
 }
 
 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 {
   return resizer_->details().bounds_change ==
       WindowResizer::kBoundsChange_Repositions;
 }
 
 void
 ToplevelWindowEventHandler::ScopedWindowResizer::OnPreWindowStateTypeChange(
     wm::WindowState* window_state,
@@ skipping 466 matching lines @@
     default:
       NOTREACHED();
   }
 }
 
 void ToplevelWindowEventHandler::ResizerWindowDestroyed() {
   CompleteDrag(DRAG_RESIZER_WINDOW_DESTROYED);
 }
 
 }  // namespace ash