Remove ActiveScriptWrappableBase::m_scriptWrappable

Thanks to Sigbjorn's CL (https://codereview.chromium.org/2577053002/),
we can now obtain a pointer to ScriptWrappable from ActiveScriptWrappable.
This CL removes ActiveScriptWrappableBase::m_scriptWrappable and
reduces sizeof(void*) from each ActiveScriptWrappable object.

BUG=

Review-Url: https://codereview.chromium.org/2578193004
Cr-Commit-Position: refs/heads/master@{#439091}
51 files changed