[mojo] Implement pipe fusion API

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

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <stdint.h>
 #include <utility>
 
 #include "base/bind.h"
 #include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
@@ skipping 696 matching lines @@
     c->D();
   }
 
   // While B & C have fallen out of scope, the pipes will remain until they are
   // flushed.
   EXPECT_FALSE(a_impl.d_called());
   run_loop.Run();
   EXPECT_TRUE(a_impl.d_called());
 }
 
+class PingTestImpl : public sample::PingTest {
+ public:
+  explicit PingTestImpl(InterfaceRequest<sample::PingTest> request)
+      : binding_(this, std::move(request)) {}
+  ~PingTestImpl() override {}
+
+ private:
+  // sample::PingTest:
+  void Ping(const PingCallback& callback) override { callback.Run(); }
+
+  Binding<sample::PingTest> binding_;
+};
+
+// Tests that FuseProxy does what it's supposed to do.
+TEST_F(InterfacePtrTest, Fusion) {
+  sample::PingTestPtr proxy;
+  PingTestImpl impl(GetProxy(&proxy));
+
+  // Create another PingTest pipe.
+  sample::PingTestPtr ptr;
+  sample::PingTestRequest request = GetProxy(&ptr);
+
+  // Fuse the new pipe to the one hanging off |impl|.
+  EXPECT_TRUE(FuseInterface(std::move(request), proxy.PassInterface()));
+
+  // Ping!
+  bool called = false;
+  base::RunLoop loop;
+  ptr->Ping([&called, &loop] {
+    called = true;
+    loop.Quit();
+  });
+  loop.Run();
+  EXPECT_TRUE(called);
+}
+
 }  // namespace
 }  // namespace test
 }  // namespace mojo