Avoid duplicate hash lookups in CustomElementScheduler::ensureCallbackQueue

We can use add() to avoid doing two hash lookups in the common case where
there's no callback queue yet (ex. setting a new attribute) and we can
also return a reference.

Review URL: https://codereview.chromium.org/206623006

git-svn-id: svn://svn.chromium.org/blink/trunk@169920 bbb929c8-8fbe-4397-9dbb-9b2b20218538
DevTools: [Frameworks] Bugfix: do StepOut in framework code after StepIn limit is up.

Bump up the limit from 10 StepIns to 20.
Add a test on framework code.

BUG=267592
R=pfeldman, yurys

Review URL: https://codereview.chromium.org/210243002

git-svn-id: svn://svn.chromium.org/blink/trunk@169921 bbb929c8-8fbe-4397-9dbb-9b2b20218538