Remove the enable_themes build flag and define.

chrome/browser/ui/browser.cc

Index: chrome/browser/ui/browser.cc
diff --git a/chrome/browser/ui/browser.cc b/chrome/browser/ui/browser.cc
index 434636764411e2cd30a0cab292636dc101fb509d..09923f08525f78cfc0d5399b3182a25d342e9095 100644
--- a/chrome/browser/ui/browser.cc
+++ b/chrome/browser/ui/browser.cc
@@ -395,7 +395,7 @@ Browser::Browser(const CreateParams& params)
   registrar_.Add(this,
                  extensions::NOTIFICATION_EXTENSION_PROCESS_TERMINATED,
                  content::NotificationService::AllSources());
-#if defined(ENABLE_THEMES)
+#if !defined(OS_ANDROID)
   registrar_.Add(
       this, chrome::NOTIFICATION_BROWSER_THEME_CHANGED,
       content::Source<ThemeService>(
@@ -1994,7 +1994,7 @@ void Browser::Observe(int type,
       break;
     }
 
-#if defined(ENABLE_THEMES)
+#if !defined(OS_ANDROID)
     case chrome::NOTIFICATION_BROWSER_THEME_CHANGED:
       window()->UserChangedTheme();
       break;