Only set MouseLockDispatcher unlocked_by_target_ after mouse lock confirmed.

content/renderer/mouse_lock_dispatcher.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 "content/renderer/mouse_lock_dispatcher.h"
 
 #include "content/common/view_messages.h"
 #include "content/renderer/render_view_impl.h"
 #include "third_party/WebKit/Source/WebKit/chromium/public/WebFrame.h"
 #include "third_party/WebKit/Source/WebKit/chromium/public/WebInputEvent.h"
@@ skipping 26 matching lines @@
   Send(new ViewHostMsg_LockMouse(routing_id(),
                                  user_gesture,
                                  unlocked_by_target_));
   unlocked_by_target_ = false;
   return true;
 }
 
 void MouseLockDispatcher::UnlockMouse(LockTarget* target) {
   if (target && target == target_ && !pending_unlock_request_) {
     pending_unlock_request_ = true;
-    unlocked_by_target_ = true;
+
+    // When a target application voluntarily unlocks the mouse we permit

[yzshen1, 2012/06/04 21:40:30]

[I don't know the exact answer, but would like to make sure that you have
considered it.]
According to the code, we are assuming that a MouseLockDispatcher object will
only be used by one "application": we don't distinguish target that sets
|unlocked_by_target_| and the one that uses it. Is that intended? Can we
guarantee that?

[scheib, 2012/06/04 23:25:40]

I considered this when designing the first patch. A web page is composing code
and plugins that may call this API. Before and after this new feature (silent
acceptance) code on a page is able to fight with other code on the page after
the user has accepted mouse lock the first time. The difference is that
previously it would fight only on user gestures, and the user would see exit
instructions.

I don't think we can put protections in place to fix poorly composed pages with
multiple sources trying to use mouse lock. It is similar to fullscreen, or
audio, or other apis: a poorly composed page can result in a poor experience.

+    // relocking the mouse silently and with no user gesture requirement.
+    // Check that the lock request is not currently pending and not yet
+    // accepted by the browser process before setting |unlocked_by_target_|.
+    if (!pending_lock_request_)
+      unlocked_by_target_ = true;
+
     Send(new ViewHostMsg_UnlockMouse(routing_id()));
   }
 }
 
 void MouseLockDispatcher::OnLockTargetDestroyed(LockTarget* target) {
   if (target == target_) {
     UnlockMouse(target);
     target_ = NULL;
   }
 }
@@ skipping 59 matching lines @@
 
   LockTarget* last_target = target_;
   target_ = NULL;
 
   // Callbacks made after all state modification to prevent reentrant errors
   // such as OnMouseLockLost() synchronously calling LockMouse().
 
   if (last_target)
     last_target->OnMouseLockLost();
 }