Fix the logic that limits the number of frames in a page.

      This check apparently doesn't run soon enough, and we can create more than the
intended limit of 1000 frames. Once we hit 1024,
NodeRareData::m_connecetedFrameCount can overflow and we no longer fully detach
Frames from their owners at teardown.

BUG=493243
TEST=WebFrameTest.MaxFramesDetach

Review URL: https://codereview.chromium.org/1180603002

git-svn-id: svn://svn.chromium.org/blink/trunk@197139 bbb929c8-8fbe-4397-9dbb-9b2b20218538