Make BackgroundContentsService start up BackgroundContents with a delay, as for ExtensionHosts.

extensions/browser/deferred_start_render_host.h

Index: extensions/browser/deferred_start_render_host.h
diff --git a/extensions/browser/deferred_start_render_host.h b/extensions/browser/deferred_start_render_host.h
new file mode 100644
index 0000000000000000000000000000000000000000..f6810c635a8e1de9c82f568afc0935d45b6c8883
--- /dev/null
+++ b/extensions/browser/deferred_start_render_host.h
@@ -0,0 +1,27 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef EXTENSIONS_BROWSER_DEFERRED_START_RENDER_HOST_H_
+#define EXTENSIONS_BROWSER_DEFERRED_START_RENDER_HOST_H_
+
+namespace extensions {
+
+// A browser component that tracks a renderer. It allows for its renderer
+// startup to be deferred, to throttle resource usage upon profile startup.
+// To be used with ExtensionHostQueue.
+//
+// Note that if BackgroundContents and ExtensionHost are unified
+// (crbug.com/77790), this interface will be no longer needed.
+class DeferredStartRenderHost {
+ public:
+  virtual ~DeferredStartRenderHost() {}
+
+  // DO NOT CALL THIS unless you're implementing an ExtensionHostQueue.
+  // Called by the ExtensionHostQueue to create the RenderView.
+  virtual void CreateRenderViewNow() = 0;
+};
+
+}  // namespace extensions
+
+#endif  // EXTENSIONS_BROWSER_DEFERRED_START_RENDER_HOST_H_