Add way to override optimization level for release build.   Will be used with valgrind to speed up the bots more.
Add way to override optimization level for release build.  
Will be used with valgrind to speed up the bots more.

This was suggested during http://codereview.chromium.org/67199, finally need it.

Review URL: http://codereview.chromium.org/155817

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@21169 0039d316-1c4b-4281-b951-d872f2087c98

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