Add toHTMLFrameElement, and use it.

We'd like to avoid bare static_cast.

BUG=none
TEST=none; no behavior changes.

Review URL: https://chromiumcodereview.appspot.com/23591013

git-svn-id: svn://svn.chromium.org/blink/trunk@156959 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Should not use setPart in a constructor.

If using setPart in a constructor, it causes an unexpected event to be dispatched, because part attribute is added.

Ported a patch uploaded in https://bugs.webkit.org/show_bug.cgi?id=116979.

BUG=280407

TEST=svg/custom/tref-with-progress-tag-setpseudo-assert.html

Review URL: https://chromiumcodereview.appspot.com/23690002

git-svn-id: svn://svn.chromium.org/blink/trunk@156960 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Update xmlhttprequest-set-responsetype.html to check json responseType

BUG=119256

Review URL: https://chromiumcodereview.appspot.com/23445015

git-svn-id: svn://svn.chromium.org/blink/trunk@156961 bbb929c8-8fbe-4397-9dbb-9b2b20218538
DevTools: Revoke undo/redo due to inconsistent behavior determining the source of storage mutation

Reverting this as discussed in CL https://codereview.chromium.org/23480006

R=pfeldman

Review URL: https://chromiumcodereview.appspot.com/23665003

git-svn-id: svn://svn.chromium.org/blink/trunk@156962 bbb929c8-8fbe-4397-9dbb-9b2b20218538