Switch optimization cflag to late-resolve the debug_optimize and release_optimize vars.
Switch optimization cflag to late-resolve the debug_optimize and release_optimize vars.

This will allow lower-level targets to change their desired optimization level.  In particular, the ffmpeg build requires this because it has problems compiling with -O0.

BUG=22307
TEST=none

Review URL: http://codereview.chromium.org/334018

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@30110 0039d316-1c4b-4281-b951-d872f2087c98

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