Check for NULL after Frame lookup in findFrameByName

This function was crashing if the FrameTree name lookup failed to find
a matching frame.

TBR=japhet@chromium.org
BUG=383845

Review URL: https://codereview.chromium.org/331633004

git-svn-id: svn://svn.chromium.org/blink/trunk@176058 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/web/WebViewImpl.cpp

@@ -2489,7 +2489,7 @@ WebFrame* WebViewImpl::findFrameByName(
         relativeToFrame = mainFrame();
     Frame* frame = toWebLocalFrameImpl(relativeToFrame)->frame();
     frame = frame->tree().find(name);
-    if (!frame->isLocalFrame())
+    if (!frame || !frame->isLocalFrame())
         return 0;
     return WebLocalFrameImpl::fromFrame(toLocalFrame(frame));
 }