Update Smali, Dx, and DexMerger tasks to use Gradle workers

This allows these tasks to run in parallel rather than in serial, leading to improved build times.

Before:

    BUILD SUCCESSFUL in 1m 3s
    317 actionable tasks: 192 executed, 125 up-to-date

After:

    BUILD SUCCESSFUL in 25s
    317 actionable tasks: 192 executed, 125 up-to-date

Change-Id: I9089a9b80cb1f0a570fc3135afbbbc6311fd4a2c
diff --git a/buildSrc/src/main/java/utils/Utils.java b/buildSrc/src/main/java/utils/Utils.java
index 7158e80..7843edd 100644
--- a/buildSrc/src/main/java/utils/Utils.java
+++ b/buildSrc/src/main/java/utils/Utils.java
@@ -17,8 +17,13 @@
     }
   }
 
+  public static File dxExecutable() {
+    String dxExecutableName = Utils.toolsDir().equals("windows") ? "dx.bat" : "dx";
+    return new File("tools/" + Utils.toolsDir() + "/dx/bin/" + dxExecutableName);
+  }
+
   public static File dexMergerExecutable() {
     String executableName = Utils.toolsDir().equals("windows") ? "dexmerger.bat" : "dexmerger";
     return new File("tools/" + Utils.toolsDir() + "/dx/bin/" + executableName);
   }
-}
\ No newline at end of file
+}