Prevent Google Mail Checker from scheduling more than one concurrent request.

Prevent Google Mail Checker from scheduling more than one concurrent request.

In the case of failures (simulated by blackholing mail.google.com in /etc/hosts,
getInboxCount was calling onError in both the onreadystatechange and onerror
handlers). Prevent this in two ways: by only invoking the callback once and by
making scheduleRequest cancel any already-scheduled requests.

BUG=88514
TEST=no

R=mpcomplete@chromium.org

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=94342

[Matt Perry, 2011-07-27 18:03:51]

LGTM