Mojo: Add NotifyBadMessage API

mojo/edk/test/mojo_test_base.h

Index: mojo/edk/test/mojo_test_base.h
diff --git a/mojo/edk/test/mojo_test_base.h b/mojo/edk/test/mojo_test_base.h
index 3d5e56e3d1581fcd800a75320a9a212eded4ba99..4f5514533a58de3112da5ab902686edb6a3bb90b 100644
--- a/mojo/edk/test/mojo_test_base.h
+++ b/mojo/edk/test/mojo_test_base.h
@@ -34,7 +34,9 @@ class MojoTestBase : public testing::Test {
 
   class ClientController {
    public:
-    ClientController(const std::string& client_name, MojoTestBase* test);
+    ClientController(const std::string& client_name,
+                     MojoTestBase* test,
+                     const ProcessErrorCallback& process_error_callback_);
     ~ClientController();
 
     MojoHandle pipe() const { return pipe_.get().value(); }
@@ -53,6 +55,13 @@ class MojoTestBase : public testing::Test {
     DISALLOW_COPY_AND_ASSIGN(ClientController);
   };
 
+  // Set the callback to handle bad messages received from test client
+  // processes. This can be set to a different callback before starting each
+  // client.
+  void set_process_error_callback(const ProcessErrorCallback& callback) {
+    process_error_callback_ = callback;
+  }
+
   ClientController& StartClient(const std::string& client_name);
 
   template <typename HandlerFunc>
@@ -144,6 +153,8 @@ class MojoTestBase : public testing::Test {
 
   std::vector<std::unique_ptr<ClientController>> clients_;
 
+  ProcessErrorCallback process_error_callback_;
+
   DISALLOW_COPY_AND_ASSIGN(MojoTestBase);
 };