[ScreenOrientation] Fix a possible crash point in ScreenOrientationProvider.

content/public/browser/screen_orientation_provider.cc

Index: content/public/browser/screen_orientation_provider.cc
diff --git a/content/public/browser/screen_orientation_provider.cc b/content/public/browser/screen_orientation_provider.cc
index 1a5350ded026755d2ef97e76a021e641ae114e71..0a930d814813ef87072e4ee7e322cf92241df9f7 100644
--- a/content/public/browser/screen_orientation_provider.cc
+++ b/content/public/browser/screen_orientation_provider.cc
@@ -28,9 +28,9 @@ 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()) {
@@ -103,11 +103,9 @@ void ScreenOrientationProvider::OnOrientationChange() {
 
 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();
 }