There's been a long-standing bug in RewriteDoWhile where it would only
call nextTemporaryId() after it had created the temporary variable.
This escalated into a null pointer dereference in the recent symbol
table refactoring, and initializing the traverser with the symbol
table was also missing.

BUG=chromium:747244
TEST=angle_unittests

Change-Id: I8987a609bb5d7d49e3c3e284fc42a2e53e38dafa
Reviewed-on: https://chromium-review.googlesource.com/580887
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>