Avoid holding a lock during destructor call when not needed
Avoid holding a lock during destructor call when not needed

I noticed this while reviewing related code.  I don't
know of an actual bug, but it is bad form to hold a
lock when calling a function (destructor) unless
necessary.  For example, if the destructor posted
a message, it might cause a hang on linux as the
posting could re-enter this helper.  It is also
possible that the task deletion will take an
extended period of time, and that can block
other concurrent posts from taking place.

r=darin

Review URL: http://codereview.chromium.org/6602024

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@76774 0039d316-1c4b-4281-b951-d872f2087c98

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