Enable the sizes attribute and srcset 'w' descriptor by default

Following the intent to ship thread[1], this CL enables the sizes attribute and srcset's 'w' descriptor by default.

BUG=357586

[1] https://groups.google.com/a/chromium.org/d/msg/blink-dev/GRfwz951FHo/RUue8U49iuwJ

Review URL: https://codereview.chromium.org/356833007

git-svn-id: svn://svn.chromium.org/blink/trunk@176988 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Do not buffer evaluateForTestInFrontend commands

evaluateForTestInFrontend may well be send from a long-running JS function and we want the message to be delivered to the front-end ASAP.

BUG=None
R=pfeldman@chromium.org

Review URL: https://codereview.chromium.org/352383003

git-svn-id: svn://svn.chromium.org/blink/trunk@176989 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Test that debugger can pause when page in an infinite loop

BUG=389161
R=alph@chromium.org

Review URL: https://codereview.chromium.org/333593007

git-svn-id: svn://svn.chromium.org/blink/trunk@176990 bbb929c8-8fbe-4397-9dbb-9b2b20218538
DevTools: Eliminate UISourceCode revision persistence across DevTools sessions

R=vsevik@chromium.org, vsevik

Review URL: https://codereview.chromium.org/346423002

git-svn-id: svn://svn.chromium.org/blink/trunk@176991 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Remove HeapSnapshot.dispose

The method is never called as we terminate the worker when we don't need a snapshot any more.

BUG=None
R=alph@chromium.org

Review URL: https://codereview.chromium.org/358853003

git-svn-id: svn://svn.chromium.org/blink/trunk@176992 bbb929c8-8fbe-4397-9dbb-9b2b20218538
HTMLMediaElement::webMediaPlayer() should never be null if m_readyState >= HAVE_METADATA (media engine error case)

BUG=382721

Review URL: https://codereview.chromium.org/330593005

git-svn-id: svn://svn.chromium.org/blink/trunk@176993 bbb929c8-8fbe-4397-9dbb-9b2b20218538