Page not fully rendered in iOS DRT snapshots
https://bugs.webkit.org/show_bug.cgi?id=137638

Reviewed by Tim Horton.

In iOS DumpRenderTree, we need to wait for a cycle of the WebThread runloop
to ensure that the page has laid out and is rendered by the time we take
the snapshot.

* DumpRenderTree/mac/DumpRenderTree.mm:
(-[DumpRenderTree _webThreadEventLoopHasRun]): Moved.
(-[DumpRenderTree _webThreadInvoked]): Moved.
(-[DumpRenderTree _waitForWebThreadThenDump]):
(dump): Use a performSelectorOnMainThread:withObject:waitUntilDone:NO to wait
for a cycle of the WebThrewd runloop. We can't just call _waitForWebThread because
that blocks on a delegate callback, and we can't dispatch_async because _waitForWebThread
relies on dispatch_async too, and the inner block won't complete until the outer block
has completed.
(dumpTestResults): Move the guts of dump() here.
(runTest): Whitespace.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@174642 268f45cc-cd09-0410-ab3c-d52691b4dbfc