Disable pre-dex for Circle CI builds

Summary:
Pre-dexing is of no value in a CI environment likes Circle CI's which builds from a clean folder each time.

Disabling it should speed up the build and reduce its memory footprint.

Reviewed By: aagnes

Differential Revision: D3340565

fbshipit-source-id: b8a4a45e094a294ca938545d815309fd8c0e6989

build.gradle

@@ -20,6 +20,7 @@ project.ext {
     compileSdkVersion = COMPILE_SDK_VERSION.toInteger()
     minSdkVersion = MIN_SDK_VERSION;
     targetSdkVersion = TARGET_SDK_VERSION;
+    preDexLibs = !project.hasProperty('disablePreDex');
 }
 
 subprojects {
@@ -50,6 +51,14 @@ 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
+        }
+    }
 }
 
 repositories {

circle.yml

@@ -6,6 +6,8 @@ machine:
   environment:
     PATH: $ANDROID_NDK:$PATH
 test:
+  override:
+    - ./gradlew assembleDebug -PdisablePreDex
   post:
     # copy test report for Circle CI to display
     - mkdir -p $CIRCLE_TEST_REPORTS/junit/