[Extensions Bindings] Correctly use a StrictMock for the IPC Sender

We have a UseStrictIPCMessageSender() method in
NativeExtensionBindingsSystemUnittest, but it wasn't being checked
when we instantiated the IPCMessageSender. Correctly check it so that
tests that want strict mocking get it.

Bug: 653596

Change-Id: Ib18945a14e0a88788bcfe9e56c530ff0ae2b36ca
Reviewed-on: https://chromium-review.googlesource.com/786900Reviewed-by: Jeremy Roman <jbroman@chromium.org>
Reviewed-by: Istiaque Ahmed <lazyboy@chromium.org>
Commit-Queue: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#519896}

extensions/renderer/native_extension_bindings_system_test_base.cc

@@ -41,10 +41,16 @@ NativeExtensionBindingsSystemUnittest::GetV8ExtensionConfiguration() {
 void NativeExtensionBindingsSystemUnittest::SetUp() {
   render_thread_ = std::make_unique<content::MockRenderThread>();
   script_context_set_ = std::make_unique<ScriptContextSet>(&extension_ids_);
-  auto ipc_message_sender = std::make_unique<TestIPCMessageSender>();
-  ipc_message_sender_ = ipc_message_sender.get();
+  std::unique_ptr<TestIPCMessageSender> message_sender;
+  if (UseStrictIPCMessageSender()) {
+    message_sender =
+        std::make_unique<testing::StrictMock<TestIPCMessageSender>>();
+  } else {
+    message_sender = std::make_unique<TestIPCMessageSender>();
+  }
+  ipc_message_sender_ = message_sender.get();
   bindings_system_ = std::make_unique<NativeExtensionBindingsSystem>(
-      std::move(ipc_message_sender));
+      std::move(message_sender));
   APIBindingTest::SetUp();
 }