Fix FindSharedFunctionInfoInScript to not optimize.

Fix FindSharedFunctionInfoInScript to not optimize.

This prevents a corner case in FindSharedFunctionInfoInScript that would cause
functions to be optimized because an intermittent GC would clear the flag
indicating whether breakpoints are present. Above method was also moved into the
Debug class because it is only used by the debugger.

R=verwaest@chromium.org

Review URL: https://chromiumcodereview.appspot.com/10914065

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@12428 ce2b1a6d-e550-0410-aec6-3dcde31c8c00