Fix crash when de-referencing the WebFrameWidget.

third_party/WebKit/Source/web/WebViewImpl.cpp

Index: third_party/WebKit/Source/web/WebViewImpl.cpp
diff --git a/third_party/WebKit/Source/web/WebViewImpl.cpp b/third_party/WebKit/Source/web/WebViewImpl.cpp
index 9f38cd1d7fae8fb22e39a071554e5ac0b8d570b0..9ab4295f3c4d42406932e3415ad9fb185dfe9155 100644
--- a/third_party/WebKit/Source/web/WebViewImpl.cpp
+++ b/third_party/WebKit/Source/web/WebViewImpl.cpp
@@ -2536,15 +2536,18 @@ void WebViewImpl::willCloseLayerTreeView() {
 }
 
 void WebViewImpl::didAcquirePointerLock() {
-  mainFrameImpl()->frameWidget()->didAcquirePointerLock();
+  if (mainFrameImpl())
+    mainFrameImpl()->frameWidget()->didAcquirePointerLock();
 }
 
 void WebViewImpl::didNotAcquirePointerLock() {
-  mainFrameImpl()->frameWidget()->didNotAcquirePointerLock();
+  if (mainFrameImpl())
+    mainFrameImpl()->frameWidget()->didNotAcquirePointerLock();
 }
 
 void WebViewImpl::didLosePointerLock() {
-  mainFrameImpl()->frameWidget()->didLosePointerLock();
+  if (mainFrameImpl())

[dcheng, 2017/03/03 23:57:24]

Please add some comments here too to document the race.

[lfg, 2017/03/06 21:31:01]

Done.

+    mainFrameImpl()->frameWidget()->didLosePointerLock();
 }
 
 // TODO(ekaramad):This method is almost duplicated in WebFrameWidgetImpl as