[chromium] delay clearing the TestRunners until the main view was deleted
https://bugs.webkit.org/show_bug.cgi?id=111823

Reviewed by Eric Seidel.

During WebViewHost::shutdown, we navigate the WebView to about:blank.
This may call into the test runners which assume that the delegate is
always non-NULL.

* DumpRenderTree/chromium/TestShell.cpp:
(TestShell::~TestShell):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@145189 268f45cc-cd09-0410-ab3c-d52691b4dbfc