Most of the variables we set in base for platform detection aren't used. This CL deletes all flags which aren't referenced in code. We also update the one use of isMac to actually use the flag instead of re-calculating it.

This removes the only use of chrome.variableName we had which makes issue 133 go away.

BUG=133

Review URL: https://codereview.appspot.com/7314086

git-svn-id: https://trace-viewer.googlecode.com/svn/trunk@209 0e6d7f2b-9903-5b78-7403-59d27f066143