Fix #207 - Add Travis CI support

As discussed in #207 (comment), requires changing to `compileSdkVersion "Google Inc.:Google APIs:21"`, because:
a) Google API emulator image is needed to run tests that require Google Play Services (see https://developers.google.com/android/guides/setup)
b) the Google API Level 23 emulator seems to have a bug that doesn't allow installing/running tests from the command line

This patch also adds a command-line option to disable pre-dexing, which is used on Travis to decrease build times (see http://tools.android.com/tech-docs/new-build-system/tips#TOC-Improving-Build-Server-performance.)

.travis.yml

@@ -0,0 +1,43 @@
+language: android
+jdk: oraclejdk7
+# Use the Travis Container-Based Infrastructure
+sudo: false
+
+cache:
+  directories:
+    - ${TRAVIS_BUILD_DIR}/gradle/caches/
+    - ${TRAVIS_BUILD_DIR}/gradle/wrapper/dists/
+
+env:
+  global:
+    - ANDROID_API_LEVEL=21
+    - ANDROID_BUILD_TOOLS_VERSION=23.0.0
+    - ANDROID_ABI=google_apis/armeabi-v7a
+    - ADB_INSTALL_TIMEOUT=20 # minutes (2 minutes by default)
+
+android:
+  components:
+    - platform-tools
+    - tools
+    - build-tools-$ANDROID_BUILD_TOOLS_VERSION
+    - android-$ANDROID_API_LEVEL
+    # For Google APIs
+    - addon-google_apis-google-$ANDROID_API_LEVEL
+    # Google Play Services
+    - extra-google-google_play_services
+    # Support library
+    - extra-android-support
+    # Latest artifacts in local repository
+    - extra-google-m2repository
+    - extra-android-m2repository
+    # Specify at least one system image
+    - sys-img-armeabi-v7a-addon-google_apis-google-$ANDROID_API_LEVEL
+
+before_script:
+  # Create and start emulator
+  - echo no | android create avd --force -n test -t "Google Inc.:Google APIs:"$ANDROID_API_LEVEL --abi $ANDROID_ABI
+  - emulator -avd test -no-skin -no-audio -no-window &
+  - android-wait-for-emulator
+
+script:
+  - ./gradlew connectedCheck -x library:signArchives -PdisablePreDex

README.md

@@ -1,4 +1,4 @@
-[![Maven Central](https://maven-badges.herokuapp.com/maven-central/com.google.maps.android/android-maps-utils/badge.svg)](https://maven-badges.herokuapp.com/maven-central/com.google.maps.android/android-maps-utils)
+[![Maven Central](https://maven-badges.herokuapp.com/maven-central/com.google.maps.android/android-maps-utils/badge.svg)](https://maven-badges.herokuapp.com/maven-central/com.google.maps.android/android-maps-utils)[![Build Status](https://travis-ci.org/googlemaps/android-maps-utils.svg?branch=master)](https://travis-ci.org/googlemaps/android-maps-utils)
 
 # Google Maps Android API utility library
 

build.gradle

@@ -7,3 +7,18 @@ buildscript {
         classpath 'com.android.tools.build:gradle:1.3.0'
     }
 }
+/**
+ * Improve build server performance by allowing disabling of pre-dexing
+ * (see http://tools.android.com/tech-docs/new-build-system/tips#TOC-Improving-Build-Server-performance.)
+ */
+project.ext.preDexLibs = !project.hasProperty('disablePreDex')
+
+subprojects {
+    project.plugins.whenPluginAdded { plugin ->
+        if ("com.android.build.gradle.AppPlugin".equals(plugin.class.name)) {
+            project.android.dexOptions.preDexLibraries = rootProject.ext.preDexLibs
+        } else if ("com.android.build.gradle.LibraryPlugin".equals(plugin.class.name)) {
+            project.android.dexOptions.preDexLibraries = rootProject.ext.preDexLibs
+        }
+    }
+}

demo/build.gradle

@@ -18,7 +18,7 @@ dependencies {
 }
 
 android {
-    compileSdkVersion 23
+    compileSdkVersion "Google Inc.:Google APIs:21"
     buildToolsVersion "23.0.0"
 
     sourceSets {

library/build.gradle

@@ -21,7 +21,7 @@ dependencies {
 
 
 android {
-    compileSdkVersion 23
+    compileSdkVersion "Google Inc.:Google APIs:21"
     buildToolsVersion "23.0.0"
 
     sourceSets {