Add test directories for dialer library build.

Update to use the same setting build-app.gradle
This CL is only for easier project setting in Android Studio, the tests
are not runnable in AS.

Change-Id: I725cfe6da9dcd9fe2c2e2e297b193a8a0da2dc9a
diff --git a/build-library.gradle b/build-library.gradle
index d353016..a2394aa 100644
--- a/build-library.gradle
+++ b/build-library.gradle
@@ -12,6 +12,11 @@
         manifest.srcFile 'AndroidManifest.xml'
         res.srcDirs = ['res']
     }
+
+    sourceSets.androidTest {
+        java.srcDirs = ['tests/src']
+        res.srcDirs = ['test/res']
+    }
 }
 
 dependencies {