[ScreenOrientation] Fix a possible crash point in ScreenOrientationProvider.

content/public/browser/screen_orientation_provider.cc

 // Copyright 2014 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/public/browser/screen_orientation_provider.h"
 
 #include "base/callback_helpers.h"
 #include "base/optional.h"
 #include "content/browser/renderer_host/render_view_host_impl.h"
 #include "content/browser/web_contents/web_contents_impl.h"
@@ skipping 10 matching lines @@
 
 ScreenOrientationProvider::ScreenOrientationProvider(WebContents* web_contents)
     : WebContentsObserver(web_contents), lock_applied_(false) {}
 
 ScreenOrientationProvider::~ScreenOrientationProvider() {
 }
 
 void ScreenOrientationProvider::LockOrientation(
     blink::WebScreenOrientationLockType orientation,
     const LockOrientationCallback& callback) {
-  // ScreenOrientation should have cancelled all pending request at this point.
-  DCHECK(on_result_callback_.is_null());

[leonhsl(Using Gerrit), 2017/01/16 11:00:18]

Although ScreenOrientation have cancelled the pending request, it can't clear
|on_result_callback_| here, |on_result_callback_| could still be non-null, we
should just reset all the pending status.

-  DCHECK(!pending_lock_orientation_.has_value());
+  // ScreenOrientation should have already cancelled all pending request at this
+  // point, so we just clear pending status here without any actual operations.
+  pending_lock_orientation_.reset();
   on_result_callback_ = callback;
 
   if (!delegate_ || !delegate_->ScreenOrientationProviderSupported()) {
     NotifyLockResult(ScreenOrientationLockResult::
                          SCREEN_ORIENTATION_LOCK_RESULT_ERROR_NOT_AVAILABLE);
     return;
   }
 
   if (delegate_->FullScreenRequired(web_contents())) {
     RenderViewHostImpl* rvhi =
@@ skipping 52 matching lines @@
 
   if (LockMatchesCurrentOrientation(pending_lock_orientation_.value())) {
     DCHECK(!on_result_callback_.is_null());
     NotifyLockResult(
         ScreenOrientationLockResult::SCREEN_ORIENTATION_LOCK_RESULT_SUCCESS);
   }
 }
 
 void ScreenOrientationProvider::NotifyLockResult(
     ScreenOrientationLockResult result) {
-  if (on_result_callback_.is_null()) {
-    pending_lock_orientation_.reset();
-    return;
+  if (!on_result_callback_.is_null()) {
+    base::ResetAndReturn(&on_result_callback_).Run(result);
   }
-  base::ResetAndReturn(&on_result_callback_).Run(result);
   pending_lock_orientation_.reset();
 }
 
 void ScreenOrientationProvider::SetDelegate(
     ScreenOrientationDelegate* delegate) {
   delegate_ = delegate;
 }
 
 void ScreenOrientationProvider::DidToggleFullscreenModeForTab(
     bool entered_fullscreen, bool will_cause_resize) {
@@ skipping 79 matching lines @@
     case blink::WebScreenOrientationLockDefault:
       NOTREACHED();
       return false;
   }
 
   NOTREACHED();
   return false;
 }
 
 } // namespace content