Move to Android Gradle Plugin 2.4.0-alpha3

Additionally, this CL adds a workaround to the change in the plugin
that no longer resolves jacoco ant dependencies unless you call
report coverage task. A workaround is to explicitly specify jacoco
ant dependency in the configuration.

Test: ./gradlew assemble
Change-Id: I6d99b99f97cf6cc8d9e89d0c1813ef9bc25c6685

dependencies.gradle

@@ -26,7 +26,7 @@ libs.espresso_core = 'com.android.support.test.espresso:espresso-core:2.3-alpha'
 libs.espresso_contrib = 'com.android.support.test.espresso:espresso-contrib:2.3-alpha'
 
 // Keep gradle plugin version in sync with ub_supportlib-master manifest.
-libs.gradle = 'com.android.tools.build:gradle:2.3.0'
+libs.gradle = 'com.android.tools.build:gradle:2.4.0-alpha3'
 
 // Other dependencies
 libs.xml_parser_apis = 'xerces:xmlParserAPIs:2.6.2'

src/main/groovy/android/support/SupportLibraryPlugin.groovy

@@ -59,6 +59,12 @@ class SupportLibraryPlugin implements Plugin<Project> {
             testInstrumentationRunner INSTRUMENTATION_RUNNER
         }
 
+        // A workaround for b.android.com/293641 where Android Gradle Plugin delays Jacoco
+        // dependency resolution if it is not set explicitly.
+        project.dependencies {
+            androidJacocoAnt "org.jacoco:org.jacoco.ant:0.7.4.201502262128"
+        }
+
         library.signingConfigs {
             debug {
                 // Use a local debug keystore to avoid build server issues.