Cleanup TTS controller unittest helper

This CL is merging the TtsControllerTestHelper class into a
base testing::Test class.

Tests are converted to use that pattern:
  TEST_F(TtsControllerTest,...)

The goal of that cleanup is to simplify the next refactoring
where a content::BrowserTaskEnvironment is required for each
test.

Change-Id: Id3757b58fc05a93ac6ebacdf3ba11ec8b234e9a9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2432751Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Commit-Queue: Etienne Bergeron <etienneb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#811851}

content/browser/speech/tts_controller_impl.cc

@@ -772,6 +772,12 @@ TtsControllerDelegate* TtsControllerImpl::GetTtsControllerDelegate() {
   }
   return nullptr;
 }
+
+void TtsControllerImpl::SetTtsControllerDelegateForTesting(
+    TtsControllerDelegate* delegate) {
+  delegate_ = delegate;
+}
+
 #endif  // defined(OS_CHROMEOS)
 
 }  // namespace content

content/browser/speech/tts_controller_impl.h

@@ -83,13 +83,7 @@ class CONTENT_EXPORT TtsControllerImpl : public TtsController,
   ~TtsControllerImpl() override;
 
  private:
-  friend class TtsControllerTestHelper;
-  FRIEND_TEST_ALL_PREFIXES(TtsControllerTest, TestTtsControllerShutdown);
-  FRIEND_TEST_ALL_PREFIXES(TtsControllerTest, TestGetMatchingVoice);
-  FRIEND_TEST_ALL_PREFIXES(TtsControllerTest,
-                           TestTtsControllerUtteranceDefaults);
-  FRIEND_TEST_ALL_PREFIXES(TtsControllerTest, TestBrowserContextRemoved);
-
+  friend class TestTtsControllerImpl;
   friend struct base::DefaultSingletonTraits<TtsControllerImpl>;
 
   // Get the platform TTS implementation (or injected mock).
@@ -151,7 +145,7 @@ class CONTENT_EXPORT TtsControllerImpl : public TtsController,
 
 #if defined(OS_CHROMEOS)
   TtsControllerDelegate* GetTtsControllerDelegate();
-
+  void SetTtsControllerDelegateForTesting(TtsControllerDelegate* delegate);
   TtsControllerDelegate* delegate_ = nullptr;
 #endif