Begin to enable extension APIs in Extension Service Worker.

extensions/common/extensions_client.h

Index: extensions/common/extensions_client.h
diff --git a/extensions/common/extensions_client.h b/extensions/common/extensions_client.h
index 7b0e9d3cff291020d882f33f8d7373bf07ddebb2..b897fb889e84c025053eacb83628950cf96fb397 100644
--- a/extensions/common/extensions_client.h
+++ b/extensions/common/extensions_client.h
@@ -131,6 +131,13 @@ class ExtensionsClient {
   virtual std::set<base::FilePath> GetBrowserImagePaths(
       const Extension* extension);
 
+  // Returns whether or not extension APIs are allowed in extension service
+  // workers.
+  // This is currently disallowed as the code to support this is work in
+  // progress.
+  // Can be overridden in tests.
+  virtual bool ExtensionAPIEnabledInExtensionServiceWorkers() const;
+
   // Return the extensions client.
   static ExtensionsClient* Get();