Remove the enable_themes build flag and define.

chrome/browser/search/instant_service.h

Index: chrome/browser/search/instant_service.h
diff --git a/chrome/browser/search/instant_service.h b/chrome/browser/search/instant_service.h
index 47d4f34d3ccd776112972a8f5b4e8a489c025def..064ca1db30aa7e21846c3eff2825d659fe0d0794 100644
--- a/chrome/browser/search/instant_service.h
+++ b/chrome/browser/search/instant_service.h
@@ -14,6 +14,7 @@
 #include "base/memory/ref_counted.h"
 #include "base/memory/weak_ptr.h"
 #include "base/observer_list.h"
+#include "build/build_config.h"
 #include "components/history/core/browser/history_types.h"
 #include "components/history/core/browser/top_sites_observer.h"
 #include "components/keyed_service/core/keyed_service.h"
@@ -145,7 +146,7 @@ class InstantService : public KeyedService,
   // Notifies the observer about the last known most visited items.
   void NotifyAboutMostVisitedItems();
 
-#if defined(ENABLE_THEMES)
+#if !defined(OS_ANDROID)
   // Theme changed notification handler.
   void OnThemeChanged();
 #endif