Add WindowFocusAllowedIndicator to the public API.

This is required to allow the chromium extension system to allow window.focus in certain situations.
BUG=325014

Review URL: https://codereview.chromium.org/108803004

git-svn-id: svn://svn.chromium.org/blink/trunk@164244 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Include m_attachedElement in MediaSourceBase::hasPendingActivity() condition.

m_attachedElement needs to be added to hasPendingActivity() so that a reference
is held the entire time it is considered "attached" to an HTMLMediaElement. This
includes the brief period it is attached, but not open yet.

BUG=330026

Review URL: https://codereview.chromium.org/112373005

git-svn-id: svn://svn.chromium.org/blink/trunk@164245 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Test for prefetch cache resetting on IDBObjectStore.clear()

Depends on crrev.com/116363006 on the Chromium side.

BUG=329971

Review URL: https://codereview.chromium.org/101503003

git-svn-id: svn://svn.chromium.org/blink/trunk@164246 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Mark media/track/track-cue-container-rendering-position as Flaky

BUG=330049
TBR=acolwell@chromium.org

Review URL: https://codereview.chromium.org/111673007

git-svn-id: svn://svn.chromium.org/blink/trunk@164247 bbb929c8-8fbe-4397-9dbb-9b2b20218538