Merged r15071 into trunk branch.

Use -O2 instead -O3 for Android build.

R=jkummerow@chromium.org

Review URL: https://chromiumcodereview.appspot.com/15821014

git-svn-id: https://v8.googlecode.com/svn/trunk@15072 ce2b1a6d-e550-0410-aec6-3dcde31c8c00