Add clang-format to CI.

.clang-format

@@ -0,0 +1,7 @@
+BasedOnStyle: Chromium
+ColumnLimit: 160
+IndentWidth: 4
+DerivePointerAlignment: false
+IndentCaseLabels: false
+PointerAlignment: Right
+SpaceAfterCStyleCast: true

.travis.yml

@@ -1,12 +1,30 @@
+sudo: required
+
 language: cpp
 compiler: g++
-before_install:
-    - sudo add-apt-repository -y ppa:ubuntu-toolchain-r/test
-    - sudo apt-get update -qq
-install:
-    - sudo apt-get install -qq g++-4.8
-    - export CXX="g++-4.8"
-script: make && sudo ./handy_test
-notifications:
-    email: true
 
+matrix:
+    include:
+        # Job1: This is the job of building project in linux os.
+      - os: linux
+        dist: trusty
+        before_install:
+            - sudo add-apt-repository -y ppa:ubuntu-toolchain-r/test
+            - sudo apt-get update -qq
+        install:
+            - sudo apt-get install -qq g++-4.8
+            - export CXX="g++-4.8"
+        script: make && sudo ./handy_test
+        notifications:
+            email: true
+
+        # Job2: This is the job of checking code style.
+      - 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 bash .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