Ensure attached frame count doesn't exceed the maximum allowed frames
https://bugs.webkit.org/show_bug.cgi?id=136457

Reviewed by Alexey Proskuryakov.

Source/WebCore:

Test: fast/frames/exponential-frames.html

* html/HTMLFrameElementBase.cpp:
(WebCore::HTMLFrameElementBase::isURLAllowed):

LayoutTests:

* fast/frames/exponential-frames-expected.txt: Added.
* fast/frames/exponential-frames.html: Added.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@174922 268f45cc-cd09-0410-ab3c-d52691b4dbfc