Makes GetComponentExtensionResourceManager() thread-safe.

extensions/browser/component_extension_resource_manager.h

Index: extensions/browser/component_extension_resource_manager.h
diff --git a/extensions/browser/component_extension_resource_manager.h b/extensions/browser/component_extension_resource_manager.h
index 1f82381e9f0db7837e9fa850b2ec031b1480a018..6495f10d32f1c71f4d674ded957bc5122e77f3d2 100644
--- a/extensions/browser/component_extension_resource_manager.h
+++ b/extensions/browser/component_extension_resource_manager.h
@@ -22,9 +22,9 @@ class ComponentExtensionResourceManager {
   // resources. Otherwise fills |resource_id|. This doesn't check if the
   // extension the resource is in is actually a component extension.
   virtual bool IsComponentExtensionResource(
-    const base::FilePath& extension_path,
-    const base::FilePath& resource_path,
-    int* resource_id) = 0;
+      const base::FilePath& extension_path,
+      const base::FilePath& resource_path,
+      int* resource_id) const = 0;
 };
 
 }  // namespace extensions