improve build server performance by allowing disabling of pre-dexing

It seems that Google is finally paying some attention to CI builds with the
emulator, they issued a recommendation:
http://tools.android.com/tech-docs/new-build-system/tips#TOC-Improving-Build-Server-performance

.gitlab-ci.yml

@@ -17,7 +17,7 @@ gradle:
     # always report on lint errors to the build log
     - sed -i -e 's,textReport .*,textReport true,' app/build.gradle
     # 'build' means assemble and check
-    - ./gradlew build || {
+    - ./gradlew build -PdisablePreDex || {
           for log in app/build/reports/*ests/*/*ml; do
               echo "read $log here:"
               cat "$log" | curl --silent -F 'clbin=<-' https://clbin.com;
@@ -40,7 +40,7 @@ gradle:
     - ./tools/wait-for-emulator
     - adb shell input keyevent 82
     - export EXITVALUE=0
-    - ADB_INSTALL_TIMEOUT=8 ./gradlew connectedCheck || {
+    - ADB_INSTALL_TIMEOUT=8 ./gradlew connectedCheck -PdisablePreDex || {
         adb -e logcat -d '*:E';
         echo "get the full logcat here:";
         adb -e logcat -d | curl --silent -F 'clbin=<-' https://clbin.com;
@@ -57,12 +57,12 @@ gradle:
 pmd:
   script:
     - export GRADLE_USER_HOME=$PWD/.gradle
-    - ./gradlew pmd
+    - ./gradlew pmd -PdisablePreDex
 
 checkstyle:
   script:
     - export GRADLE_USER_HOME=$PWD/.gradle
-    - ./gradlew checkstyle
+    - ./gradlew checkstyle -PdisablePreDex
 
 tools:
   script:

build.gradle

@@ -7,3 +7,19 @@ buildscript {
         classpath files('libs/gradle-witness.jar')
     }
 }
+
+/**
+ * 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
+    }
+  }
+}