JavaScript shouldn't be called during LifecycleObsever traversal

This change adds a couple of RELEASE_ASSERT() to detect wrong
JS function invocation during LifeycleObserver traversal.

Crash reports for this kind of violation (like bug 297482) is cryptic
because JavaScript invocation hides underlying stack trace.
By ASSERT-ing before such invocations should reveal better stack trace
to diagnose the problem.

R=haraken@chromium.org,abarth@chromium.org
BUG=297482
TEST=none

Review URL: https://chromiumcodereview.appspot.com/25236002

git-svn-id: svn://svn.chromium.org/blink/trunk@158533 bbb929c8-8fbe-4397-9dbb-9b2b20218538