Only enable Hotwords when extensions are enabled.

chrome/chrome_browser_ui.gypi

Index: chrome/chrome_browser_ui.gypi
diff --git a/chrome/chrome_browser_ui.gypi b/chrome/chrome_browser_ui.gypi
index 9d1413ecc7add144d9160b8da4f53b5e07bf0d41..1239cbc81c1cfd6e508ab30c2a7fa1046fe16fde 100644
--- a/chrome/chrome_browser_ui.gypi
+++ b/chrome/chrome_browser_ui.gypi
@@ -1133,8 +1133,6 @@
       'browser/ui/webui/version_handler.h',
       'browser/ui/webui/version_ui.cc',
       'browser/ui/webui/version_ui.h',
-      'browser/ui/webui/voicesearch_ui.cc',
-      'browser/ui/webui/voicesearch_ui.h',
       'browser/ui/webui/welcome_handler_android.cc',
       'browser/ui/webui/welcome_handler_android.h',
       'browser/ui/webui/welcome_ui_android.cc',
@@ -2526,6 +2524,10 @@
       'browser/ui/profile_error_dialog.cc',
       'browser/ui/profile_error_dialog.h',
     ],
+    'chrome_browser_ui_extensions_sources': [
+      'browser/ui/webui/voicesearch_ui.cc',
+      'browser/ui/webui/voicesearch_ui.h',
+    ],
   },
   'targets': [
     {
@@ -2928,6 +2930,9 @@
             }],
           ],
         }],
+        ['enable_extensions==1', {
+          'sources': [ '<@(chrome_browser_ui_extensions_sources)' ],
+        }],
         ['enable_google_now==1 and OS!="android"', {
           'sources': [ '<@(chrome_browser_ui_google_now_non_android_sources)' ],
         }],