Remove TreatNullAs=NullString for HTMLSelectElement

http://whatwg.org/html#htmlselectelement

The value attribute returns "" when there is no selected child
<option> element, so add another test to verify that null
stringifies to "null" on setting.

The tests for the updated properties pass in Firefox Nightly, IE11
Release Preview and Opera 12.16.

BUG=310298

Review URL: https://codereview.chromium.org/101573002

git-svn-id: svn://svn.chromium.org/blink/trunk@163087 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Revert "Move V8ValueCache to new-style weak callbacks"

This reverts commit c5d1bea5602dd5444ef066724780d78e06a60f2f.

CL: https://codereview.chromium.org/98883002/

Example of crash this CL is suspected to have caused:
https://storage.googleapis.com/chromium-layout-test-archives/WebKit_Mac10_6__dbg_/10131/layout-test-results/results.html

TBR=jochen@chromium.org
BUG=None

Review URL: https://codereview.chromium.org/101953002

git-svn-id: svn://svn.chromium.org/blink/trunk@163089 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Remove unusued typedef in InspectorMemoryAgent.h

Minor cleanup.
BUG=none.

Review URL: https://codereview.chromium.org/101163002

git-svn-id: svn://svn.chromium.org/blink/trunk@163090 bbb929c8-8fbe-4397-9dbb-9b2b20218538