Verify that ComponentExtensionResourceManager exists before using it.

App_shell doesn't have a ComponentExtensionResourceManager implementation, so we need to check if it's available before using it.

BUG=352293

Review URL: https://codereview.chromium.org/615703002

Cr-Commit-Position: refs/heads/master@{#297299}

extensions/browser/api/execute_code_function.cc

@@ -206,9 +206,11 @@ bool ExecuteCodeFunction::RunAsync() {
   }
 
   int resource_id;
-  if (ExtensionsBrowserClient::Get()
-          ->GetComponentExtensionResourceManager()
-          ->IsComponentExtensionResource(resource_.extension_root(),
+  ComponentExtensionResourceManager* component_extension_resource_manager =
+      ExtensionsBrowserClient::Get()->GetComponentExtensionResourceManager();
+  if (component_extension_resource_manager &&
+      component_extension_resource_manager->IsComponentExtensionResource(
+          resource_.extension_root(),
           resource_.relative_path(),
           &resource_id)) {
     const ResourceBundle& rb = ResourceBundle::GetSharedInstance();