diff --git a/build/tree_truth.sh b/build/tree_truth.sh
new file mode 100755
index 00000000000000..03d0523bd2ffba
--- /dev/null
+++ b/build/tree_truth.sh
@@ -0,0 +1,101 @@
+#!/bin/bash
+# Copyright 2013 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+#
+# Script for printing recent commits in a buildbot run.
+
+# Return the sha1 of the given tag.  If not present, return "".
+# $1: path to repo
+# $2: tag name
+tt_sha1_for_tag() {
+  oneline=$(cd $1 && git log -1 $2 --format='%H' 2>/dev/null)
+  if [ $? -eq 0 ] ; then
+    echo $oneline
+  fi
+}
+
+# Return the sha1 of HEAD, or ""
+# $1: path to repo
+tt_sha1_for_head() {
+  ( cd $1 && git log HEAD -n1 --format='%H' | cat )
+}
+
+# For the given repo, set tag to HEAD.
+# $1: path to repo
+# $2: tag name
+tt_tag_head() {
+  ( cd $1 && git tag -f $2 )
+}
+
+# For the given repo, delete the tag.
+# $1: path to repo
+# $2: tag name
+tt_delete_tag() {
+  ( cd $1 && git tag -d $2 )
+}
+
+# For the given repo, set tag to "three commits ago" (for testing).
+# $1: path to repo
+# $2: tag name
+tt_tag_three_ago() {
+ local sh=$(cd $1 && git log --pretty=oneline -n 3 | tail -1 | awk '{print $1}')
+  ( cd $1 && git tag -f $2 $sh )
+}
+
+# List the commits between the given tag and HEAD.
+# If the tag does not exist, only list the last few.
+# If the tag is at HEAD, list nothing.
+# Output format has distinct build steps for repos with changes.
+# $1: path to repo
+# $2: tag name
+# $3: simple/short repo name to use for display
+tt_list_commits() {
+  local tag_sha1=$(tt_sha1_for_tag $1 $2)
+  local head_sha1=$(tt_sha1_for_head $1)
+  local display_name=$(echo $3 | sed 's#/#_#g')
+  if [ "${tag_sha1}" = "${head_sha1}" ] ; then
+    return
+  fi
+  if [ "${tag_sha1}" = "" ] ; then
+    echo "@@@BUILD_STEP Recent commits in repo $display_name@@@"
+    echo "NOTE: git tag was not found so we have no baseline."
+    echo "Here are some recent commits, but they may not be new for this build."
+    ( cd $1 && git log -n 10 --stat | cat)
+  else
+    echo "@@@BUILD_STEP New commits in repo $display_name@@@"
+    ( cd $1 && git log -n 500 $2..HEAD --stat | cat)
+  fi
+}
+
+# Clean out the tree truth tags in all repos.  For testing.
+tt_clean_all() {
+ for project in $@; do
+   tt_delete_tag $CHROME_SRC/../$project tree_truth
+ done
+}
+
+# Print tree truth for all clank repos.
+tt_print_all() {
+ for project in $@; do
+   local full_path=$CHROME_SRC/../$project
+   tt_list_commits $full_path tree_truth $project
+   tt_tag_head $full_path tree_truth
+ done
+}
+
+# Print a summary of the last 10 commits for each repo.
+tt_brief_summary() {
+  echo "@@@BUILD_STEP Brief summary of recent CLs in every branch@@@"
+  for p in $@; do
+    echo $project
+    (cd $CHROME_SRC/../$p && git log -n 10 --format="   %H %s   %an, %ad" | cat)
+    echo "================================================================="
+  done
+}
+
+CHROME_SRC=$1
+shift
+PROJECT_LIST=$@
+tt_brief_summary $PROJECT_LIST
+tt_print_all $PROJECT_LIST