Move Extension into extensions namespace

chrome/browser/extensions/convert_web_app.h

Index: chrome/browser/extensions/convert_web_app.h
diff --git a/chrome/browser/extensions/convert_web_app.h b/chrome/browser/extensions/convert_web_app.h
index 0ce2814c6fb837f8982daf261abed86e2fb471b4..4aecb5d347926f86f43c709d55d41c055c004bd6 100644
--- a/chrome/browser/extensions/convert_web_app.h
+++ b/chrome/browser/extensions/convert_web_app.h
@@ -10,12 +10,15 @@
 
 #include "base/memory/ref_counted.h"
 
-class Extension;
 
 namespace base {
 class Time;
 }
 
+namespace extensions {
+class Extension;
+}
+
 struct WebApplicationInfo;
 
 // Generates a version number for an extension from a time. The goal is to make
@@ -36,7 +39,7 @@ std::string ConvertTimeToExtensionVersion(const base::Time& time);
 // NOTE: This function does file IO and should not be called on the UI thread.
 // NOTE: The caller takes ownership of the directory at extension->path() on the
 // returned object.
-scoped_refptr<Extension> ConvertWebAppToExtension(
+scoped_refptr<extensions::Extension> ConvertWebAppToExtension(
     const WebApplicationInfo& web_app_info,
     const base::Time& create_time);