Remove pseudo-idle notification for main frame reload.

GC work after page reload introduces unnecessary pause and regresses Octane (see bug).

This CL might increase memory usage in the case when page is reloaded many times within a small timeframe. If there are such regressions, then they should be fixed by adjusting V8 GC heuristics and not sending pseudo-idle notification.

This CL does not regress SunSpider benchmark.

BUG=404020

Review URL: https://codereview.chromium.org/544593002

git-svn-id: svn://svn.chromium.org/blink/trunk@181394 bbb929c8-8fbe-4397-9dbb-9b2b20218538