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

This reverts commit 1ce7cbe264e9a3e2e2a4a29ef5ba0ab5b5a0c4ac.

This just causes the crashes in bug 331580 to come back, the mystery
crashes remain...

TBR=dcheng@chromium.org

Review URL: https://codereview.chromium.org/109023012

git-svn-id: svn://svn.chromium.org/blink/trunk@164479 bbb929c8-8fbe-4397-9dbb-9b2b20218538