Revert "Allow WebFrame creators to pass in a null client."

This reverts commit 7116fbe7b40ed226c6c17c409cbed402ab76390e.

Made everything crash on Mac Debug.
http://build.chromium.org/p/chromium.webkit/builders/WebKit%20Mac10.6%20%28dbg%29/builds/11037/steps/webkit_tests

TBR=dcheng@chromium.org

Review URL: https://codereview.chromium.org/124433002

git-svn-id: svn://svn.chromium.org/blink/trunk@164478 bbb929c8-8fbe-4397-9dbb-9b2b20218538