Move ".crx"/".pem" constants and extension_filenames constants into extensions/common/constants.cc.

chrome/common/extensions/extension.h

Index: chrome/common/extensions/extension.h
diff --git a/chrome/common/extensions/extension.h b/chrome/common/extensions/extension.h
index 3840266da7b6ac4052b1c852bf572cb141475cac..394b927e9cdcb132f661050ca6a8fcc1e5242af2 100644
--- a/chrome/common/extensions/extension.h
+++ b/chrome/common/extensions/extension.h
@@ -178,9 +178,6 @@ class Extension : public base::RefCountedThreadSafe<Extension> {
   // Checks to see if the extension has a valid ID.
   static bool IdIsValid(const std::string& id);
 
-  // Returns true if the specified file is an extension.
-  static bool IsExtension(const base::FilePath& file_name);
-
   // See Type definition in Manifest.
   Manifest::Type GetType() const;