Enable clang format in CI

.clang-format

@@ -0,0 +1,7 @@
+BasedOnStyle: Chromium
+ColumnLimit: 120
+IndentWidth: 4
+DerivePointerAlignment: false
+IndentCaseLabels: false
+PointerAlignment: Right
+SpaceAfterCStyleCast: true

.travis.yml

@@ -30,4 +30,15 @@ script:
 matrix:
   include:
     - os: linux
-      env: CUSTOM_JDK="oraclejdk8"
+      env: CUSTOM_JDK="oraclejdk8"
+
+    # This is the job to check code format.
+    - os: linux
+      dist: trusty
+      env: LINT=1 PYTHON=2.7
+      before_install:
+        - sudo apt-get update -qq
+        - sudo apt-get install -qq clang-format-3.8
+      install: []
+      script:
+        - sudo sh .travis/check-git-clang-format.sh

.travis/check-git-clang-format.sh

@@ -0,0 +1,18 @@
+#!/bin/bash
+
+ if [ "$TRAVIS_PULL_REQUEST" == "true" ] ; then
+    base_commit="$TRAVIS_BRANCH"
+else
+    base_commit="HEAD^"
+fi
+
+ output="$(sudo python .travis/git-clang-format --binary clang-format-3.8 --commit $base_commit --diff)"
+
+ if [ "$output" == "no modified files to format" ] || [ "$output" == "clang-format did not modify any files" ] ; then
+    echo "clang-format passed."
+    exit 0
+else
+    echo "clang-format failed."
+    echo "$output"
+    exit 1
+fi