Remove unused object field that broke some builds

It's not allowed to have unused object fields but the compiler
can't always know if a field is unused. In jumbo builds it will
know more so sometimes those detect cases that normal compilation
won't see. In this case a field only used in ChromeOS builds.

In file included from gen/chrome/browser/browser_jumbo_1.cc:80:
In file included from ./../../chrome/browser/chrome_content_browser_client.cc:428:
In file included from ../../chrome/browser/speech/extension_api/tts_engine_delegate_factory_impl.h:10:
../../chrome/browser/speech/extension_api/tts_engine_delegate_impl.h:35:28: error: private field 'browser_context_' is not used [-Werror,-Wunused-private-field]

  content::BrowserContext* browser_context_;
                           ^

TBR=dmazzoni@chromium.org

Bug: 862710
Change-Id: I4eca7b940ad49fb44ec61ec513ba54db55f4914c
Reviewed-on: https://chromium-review.googlesource.com/1225759
Commit-Queue: Daniel Bratell <bratell@opera.com>
Reviewed-by: Daniel Bratell <bratell@opera.com>
Reviewed-by: Jinho Bang <jinho.bang@samsung.com>
Cr-Commit-Position: refs/heads/master@{#591337}

chrome/browser/speech/extension_api/tts_engine_delegate_impl.cc

@@ -61,7 +61,11 @@ void WarnIfMissingPauseOrResumeListener(Profile* profile,
 
 TtsEngineDelegateImpl::TtsEngineDelegateImpl(
     content::BrowserContext* browser_context)
-    : browser_context_(browser_context) {}
+#if defined(OS_CHROMEOS)
+    : browser_context_(browser_context)
+#endif  // OS_CHROMEOS
+{
+}
 
 void TtsEngineDelegateImpl::GetVoices(content::BrowserContext* browser_context,
                                       std::vector<VoiceData>* out_voices) {

chrome/browser/speech/extension_api/tts_engine_delegate_impl.h

@@ -7,6 +7,7 @@
 
 #include <vector>
 
+#include "build/build_config.h"
 #include "chrome/browser/speech/tts_engine_delegate.h"
 #include "chrome/common/extensions/api/speech/tts_engine_manifest_handler.h"
 #include "components/keyed_service/core/keyed_service.h"
@@ -32,7 +33,9 @@ class TtsEngineDelegateImpl : public TtsEngineDelegate, public KeyedService {
   friend class TtsEngineDelegateFactoryImpl;
   explicit TtsEngineDelegateImpl(content::BrowserContext* browser_context);
 
+#if defined(OS_CHROMEOS)
   content::BrowserContext* browser_context_;
+#endif  // OS_CHROMEOS
 };
 
 #endif  // CHROME_BROWSER_SPEECH_EXTENSION_API_TTS_ENGINE_DELEGATE_IMPL_H_