Move Extension into extensions namespace

chrome/browser/sync/glue/theme_util.h

Index: chrome/browser/sync/glue/theme_util.h
diff --git a/chrome/browser/sync/glue/theme_util.h b/chrome/browser/sync/glue/theme_util.h
index 988b39d6d03e67a0ae1029335c5f017410df2cb4..a502b7362e08fbe20a2584800952d745e0ead76a 100644
--- a/chrome/browser/sync/glue/theme_util.h
+++ b/chrome/browser/sync/glue/theme_util.h
@@ -6,9 +6,12 @@
 #define CHROME_BROWSER_SYNC_GLUE_THEME_UTIL_H_
 #pragma once
 
-class Extension;
 class Profile;
 
+namespace extensions {
+class Extension;
+}
+
 namespace sync_pb {
 class ThemeSpecifics;
 }  // sync_pb
@@ -41,7 +44,7 @@ void GetThemeSpecificsFromCurrentTheme(
 
 // Exposed only for testing.
 void GetThemeSpecificsFromCurrentThemeHelper(
-    const Extension* current_theme,
+    const extensions::Extension* current_theme,
     bool is_system_theme_distinct_from_default_theme,
     bool use_system_theme_by_default,
     sync_pb::ThemeSpecifics* theme_specifics);