Remove lifetime hack in WebFrameImpl::createChildFrame().

Reversing the ownership becomes somewhat simpler with this change, since
the code will no longer have to deal with two different ownership models.

This patch adds a new minimal implementation of WebFrameClient intended
for tests that need to load URLs with frames, and fixes/updates several
tests that broke as a result of removing the lifetime hack. Most tests
have just been updated to use FrameTestHelpers directly, simplifying
them.

BUG=329266

Review URL: https://codereview.chromium.org/98693014

git-svn-id: svn://svn.chromium.org/blink/trunk@164135 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Remove dead code in SerializedScriptValue, ScriptValue, and Navigator

BUG=

Review URL: https://codereview.chromium.org/107323004

git-svn-id: svn://svn.chromium.org/blink/trunk@164136 bbb929c8-8fbe-4397-9dbb-9b2b20218538