Add dexmerger support for Windows

This CL adds a dexmerger.bat script that uses the
already present dx.jar file in order to be able to
build tests that rely on this tool, namely the smali
tests.

Bug:

Change-Id: I4b69f6b60c7fc7e042b82c36657e5fcf22a0239a
diff --git a/buildSrc/src/main/java/utils/Utils.java b/buildSrc/src/main/java/utils/Utils.java
index 4cbc90c..7158e80 100644
--- a/buildSrc/src/main/java/utils/Utils.java
+++ b/buildSrc/src/main/java/utils/Utils.java
@@ -3,6 +3,8 @@
 // BSD-style license that can be found in the LICENSE file.
 package utils;
 
+import java.io.File;
+
 public class Utils {
   public static String toolsDir() {
     String osName = System.getProperty("os.name");
@@ -14,4 +16,9 @@
       return "linux";
     }
   }
-}
+
+  public static File dexMergerExecutable() {
+    String executableName = Utils.toolsDir().equals("windows") ? "dexmerger.bat" : "dexmerger";
+    return new File("tools/" + Utils.toolsDir() + "/dx/bin/" + executableName);
+  }
+}
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