[devtools] Avoid Security Error on view-shown- events

If an Extension SidebarPane onShown listener is registered
for a setExpression sidebar extensions, the event causes
Security Errors. The call from WebInspector.ExtensionNotifierView
to WebInspector.extensionServer.notifyViewShown() does not supply
frameIndex, window.parent.frames[undefined] throws.

Add a test for this case and fire the event w/o frame per docs.

BUG=

Review URL: https://codereview.chromium.org/24455002

git-svn-id: svn://svn.chromium.org/blink/trunk@158745 bbb929c8-8fbe-4397-9dbb-9b2b20218538