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

extensions/browser/delayed_start_render_host.h

Index: extensions/browser/delayed_start_render_host.h
diff --git a/extensions/browser/delayed_start_render_host.h b/extensions/browser/delayed_start_render_host.h
new file mode 100644
index 0000000000000000000000000000000000000000..8b4d71b91caffb4b5fe0553bfbd0734b3f9ab56e
--- /dev/null
+++ b/extensions/browser/delayed_start_render_host.h
@@ -0,0 +1,24 @@
+// 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_DELAYED_START_RENDER_HOST_H_
+#define EXTENSIONS_BROWSER_DELAYED_START_RENDER_HOST_H_
+
+namespace extensions {
+
+// A browser component that tracks a renderer. It allows for its renderer
+// startup to be delayed, 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 DelayedStartRenderHost {

[Yoyo Zhou, 2015/02/18 22:53:18]

This is not my favoritest name - suggestions welcome.

[Devlin, 2015/02/18 23:22:12]

Even though the DelayedStart part of this is a pretty central detail of the
implementation, I think it actually is still an implementation detail here, and
is more suited to a comment on the ExtensionHostQueue (imagine, for instance, if
we had a queue that just immediately created everything).  So maybe just
ExtensionRenderViewCreator?  Not sure that's much better...

[Yoyo Zhou, 2015/02/19 02:55:37]

I came up with the slightly tautological ExtensionQueueHost. Sadly, the queue is
still an implementation detail... I'll keep thinking about it.

[Devlin, 2015/02/19 16:41:43]

Also, I think that having ExtensionQueueHost and ExtensionHostQueue is a little,
uh, much. I'll keep thinking, too.

+ public:
+  // Called by the ExtensionHostQueue to create the RenderView.
+  virtual void CreateRenderViewNow() = 0;

[Devlin, 2015/02/18 23:22:12]

virtual destructor?

[Yoyo Zhou, 2015/02/19 02:55:37]

Done.

+};
+
+}  // namespace extensions
+
+#endif  // EXTENSIONS_BROWSER_DELAYED_START_RENDER_HOST_H_