Support generation of Parcelable nano messages.

This CL adds the "parcelable_messages" option. When enabled, all
generated message classes will conform to the Android Parcelable
contract. This is achieved by introducing a new parent class for
generated classes which implements the required functionality.

Since the store_unknown_fields option also makes use of a superclass,
ExtendableMessageNano, we have two versions of the new Parcelable
superclass: one extending MessageNano, and one extending
ExtendableMessageNano. These classes are otherwise identical.

As these classes depend on Android framework jars, they are not
included in the host .jar build of the nanoproto library.

Finally, add a test suite for running tests of Android-specific
functionality, as this cannot be done on a desktop JVM.

Change-Id: Icc2a257f03317e947f7078dbb9857c3286857497
diff --git a/build.gradle b/build.gradle
index 1efd4bf..95c9b1d 100644
--- a/build.gradle
+++ b/build.gradle
@@ -1,4 +1,3 @@
-=======
 /*
  * Copyright (C) 2013 The Android Open Source Project
  *
@@ -25,17 +24,33 @@
 sourceSets {
     micro {
         java {
-            srcDirs = ['java/src/main/java/com/google/protobuf/micro']
+            srcDirs = ['java/src/main/java/']
+            include("com/google/protobuf/micro/*")
         }
     }
 
     nano {
         java {
-            srcDirs = ['java/src/main/java/com/google/protobuf/nano']
+            srcDirs = [
+                    'java/src/main/java/',
+                    'java/src/device/main/java/'
+            ]
+            include("com/google/protobuf/nano/**")
         }
     }
 }
 
+if (project == rootProject) {
+    ext.getAndroidPrebuilt = { apiLevel ->
+        files("$rootDir/../../prebuilts/sdk/$apiLevel/android.jar")
+    }
+}
+
+dependencies {
+    compile getAndroidPrebuilt('8')
+    nanoCompile getAndroidPrebuilt('8')
+}
+
 jar {
     from sourceSets.nano.output, sourceSets.micro.output
     baseName "libprotobuf"