Extensions: Consolidate extension id hashing / searching.

extensions/common/extension.h

Index: extensions/common/extension.h
diff --git a/extensions/common/extension.h b/extensions/common/extension.h
index 1e1e52cc039c580a58dcee3f27509e63b495e076..e507e705132454b8ad328028f4e87e3c5e1e4d72 100644
--- a/extensions/common/extension.h
+++ b/extensions/common/extension.h
@@ -318,6 +318,9 @@ class Extension : public base::RefCountedThreadSafe<Extension> {
     return permissions_data_.get();
   }
 
+  // Returns a hash for the extension id.
+  std::string HashedIdInHex() const;
+
   // Appends |new_warning[s]| to install_warnings_.
   void AddInstallWarning(const InstallWarning& new_warning);
   void AddInstallWarnings(const std::vector<InstallWarning>& new_warnings);