Fix tree check in merge-to-branch script.

BUG=
R=ulan@chromium.org

Review URL: https://codereview.chromium.org/138963006

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@18648 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

tools/merge-to-branch.sh

@@ -243,7 +243,9 @@ if [ $START_STEP -le $CURRENT_STEP ] ; then
   git checkout $BRANCHNAME \
     || die "cannot ensure that the current branch is $BRANCHNAME"
   wait_for_lgtm
-  PRESUBMIT_TREE_CHECK="skip" git cl dcommit \
+  PRESUBMIT_TREE_CHECK="skip" git cl presubmit \
+    || die "presubmit failed"
+  PRESUBMIT_TREE_CHECK="skip" git cl dcommit --bypass-hooks \
     || die "failed to commit to $MERGE_TO_BRANCH"
 fi