Improve HTMLMediaElement exception messages.

This patch takes care of most of the exceptions in HTMLMediaElement. A
few run through a helper function after being caused in other files; a
future patch will route reasonable messages through to the point where
they're thrown.

BUG=270033

Review URL: https://codereview.chromium.org/164193007

git-svn-id: svn://svn.chromium.org/blink/trunk@167189 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Remove unused bool in Document

R=adamk@chromium.org

Review URL: https://codereview.chromium.org/166443002

git-svn-id: svn://svn.chromium.org/blink/trunk@167190 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Fix assertion fail in htmlediting.

r162687 causes this assertion, because the revision broke the assumption that
the node owning a renderer is editable.

BUG=343037
TEST=editing/selection/table-element-crash.html

Review URL: https://codereview.chromium.org/130613006

git-svn-id: svn://svn.chromium.org/blink/trunk@167191 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Improve exception messages in core/svg.

BUG=270033

Review URL: https://codereview.chromium.org/166393002

git-svn-id: svn://svn.chromium.org/blink/trunk@167192 bbb929c8-8fbe-4397-9dbb-9b2b20218538
DevTools: Remove the settings->extensions dependency

R=eustas, pfeldman

Review URL: https://codereview.chromium.org/163183008

git-svn-id: svn://svn.chromium.org/blink/trunk@167193 bbb929c8-8fbe-4397-9dbb-9b2b20218538