Avoids releasing pointer grab prematurely

ui/views/widget/desktop_aura/x11_whole_screen_move_loop.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 "ui/views/widget/desktop_aura/x11_whole_screen_move_loop.h"
 
 #include <X11/Xlib.h>
 // Get rid of a macro from Xlib.h that conflicts with Aura's RootWindow class.
 #undef RootWindow
 
@@ skipping 76 matching lines @@
 
   return POST_DISPATCH_NONE;
 }
 
 ////////////////////////////////////////////////////////////////////////////////
 // DesktopWindowTreeHostLinux, aura::client::WindowMoveClient implementation:
 
 bool X11WholeScreenMoveLoop::RunMoveLoop(aura::Window* source,
                                          gfx::NativeCursor cursor) {
   // Start a capture on the host, so that it continues to receive events during
-  // the drag.
-  ScopedCapturer capturer(source->GetDispatcher()->host());
+  // the drag. This may be second time we are capturing the mouse events - the
+  // first being when a mouse is first pressed. That first capture needs to be
+  // released before the call to GrabPointerWithCursor below, otherwise it may
+  // get released while we still need the pointer grab, which is why we restrict
+  // the scope here.
+  {
+    ScopedCapturer capturer(source->GetDispatcher()->host());
 
-  DCHECK(!in_move_loop_);  // Can only handle one nested loop at a time.
-  in_move_loop_ = true;
+    DCHECK(!in_move_loop_);  // Can only handle one nested loop at a time.
+    in_move_loop_ = true;
 
-  XDisplay* display = gfx::GetXDisplay();
+    XDisplay* display = gfx::GetXDisplay();
 
-  grab_input_window_ = CreateDragInputWindow(display);
-  if (!drag_image_.isNull())
-    CreateDragImageWindow();
-  base::MessagePumpX11::Current()->AddDispatcherForWindow(
-      this, grab_input_window_);
-
+    grab_input_window_ = CreateDragInputWindow(display);
+    if (!drag_image_.isNull())
+      CreateDragImageWindow();
+    base::MessagePumpX11::Current()->AddDispatcherForWindow(
+        this, grab_input_window_);
+    // Releasing ScopedCapturer ensures that any other instance of
+    // X11ScopedCapture will not prematurely release grab that will be acquired
+    // below.
+  }
+  // TODO(varkha): Consider integrating GrabPointerWithCursor with
+  // ScopedCapturer to avoid possibility of logically keeping multiple grabs.
   if (!GrabPointerWithCursor(cursor))
     return false;
 
   // We are handling a mouse drag outside of the aura::RootWindow system. We
   // must manually make aura think that the mouse button is pressed so that we
   // don't draw extraneous tooltips.
   aura::Env* env = aura::Env::GetInstance();
   if (!env->IsMouseButtonDown()) {
     env->set_mouse_button_flags(ui::EF_LEFT_MOUSE_BUTTON);
     should_reset_mouse_flags_ = true;
@@ skipping 119 matching lines @@
   image->SetBounds(0, 0, drag_image_.width(), drag_image_.height());
   widget->SetContentsView(image);
 
   widget->Show();
   widget->GetNativeWindow()->layer()->SetFillsBoundsOpaquely(false);
 
   drag_widget_.reset(widget);
 }
 
 }  // namespace views