Undeprecate Event.returnValue and Attr.specified

The usage of these is so high that complaining about them is likely to
make developers ignore console warnings:
http://www.chromestatus.com/metrics/feature/timeline/popularity/137
http://www.chromestatus.com/metrics/feature/timeline/popularity/162

Spec bugs filed to maybe make them standard instead:
https://www.w3.org/Bugs/Public/show_bug.cgi?id=25001
https://www.w3.org/Bugs/Public/show_bug.cgi?id=25002

Discussion on blink-dev:
https://groups.google.com/a/chromium.org/d/msg/blink-dev/eplNSf8oDfw/0kB2gD0lQHgJ

BUG=none

Review URL: https://codereview.chromium.org/194173002

git-svn-id: svn://svn.chromium.org/blink/trunk@168918 bbb929c8-8fbe-4397-9dbb-9b2b20218538
DevTools: protocol error responses to return error details.

This patch adds ExceptionState::message() method to return exception
message. The method is used to generate protocol error responses.

BUG=

Review URL: https://codereview.chromium.org/190673002

git-svn-id: svn://svn.chromium.org/blink/trunk@168919 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Oilpan: Fix crashes introduced by style sheet content cache weak processing.

The problem is that null values are put in the stylesheet content cache
(which is bad and is a leak, but we should be able to deal with it).
This mimics the current behavior where you leak if the weak member is
null. I'll see if I can restructure the code to get rid of the leak
in this code for good.

R=erik.corry@gmail.com, oilpan-reviews@chromium.org
BUG=

Review URL: https://codereview.chromium.org/194473004

git-svn-id: svn://svn.chromium.org/blink/trunk@168920 bbb929c8-8fbe-4397-9dbb-9b2b20218538