Generate a templated Clone method for all mojo structs.

mojo/public/cpp/bindings/tests/pickle_unittest.cc

Index: mojo/public/cpp/bindings/tests/pickle_unittest.cc
diff --git a/mojo/public/cpp/bindings/tests/pickle_unittest.cc b/mojo/public/cpp/bindings/tests/pickle_unittest.cc
index 0b6a795e19dceea7154bf40d9acc8fa33e3faae1..d5f4fc50a8a02b0b91d9b4065469d1dc33653ea3 100644
--- a/mojo/public/cpp/bindings/tests/pickle_unittest.cc
+++ b/mojo/public/cpp/bindings/tests/pickle_unittest.cc
@@ -59,9 +59,9 @@ class ChromiumPicklePasserImpl : public PicklePasser {
   ChromiumPicklePasserImpl() {}
 
   // mojo::test::PicklePasser:
-  void PassPickle(const PickledStructChromium& pickle,
+  void PassPickle(PickledStructChromium pickle,
                   const PassPickleCallback& callback) override {
-    callback.Run(pickle);
+    callback.Run(std::move(pickle));
   }
 
   void PassPickleContainer(
@@ -87,9 +87,9 @@ class BlinkPicklePasserImpl : public blink::PicklePasser {
   BlinkPicklePasserImpl() {}
 
   // mojo::test::blink::PicklePasser:
-  void PassPickle(const PickledStructBlink& pickle,
+  void PassPickle(PickledStructBlink pickle,
                   const PassPickleCallback& callback) override {
-    callback.Run(pickle);
+    callback.Run(std::move(pickle));
   }
 
   void PassPickleContainer(