Add the Copresence API.

chrome/browser/extensions/api/copresence/copresence_util.h

+// Copyright 2014 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 CHROME_BROWSER_EXTENSIONS_API_COPRESENCE_COPRESENCE_UTIL_H_
+#define CHROME_BROWSER_EXTENSIONS_API_COPRESENCE_COPRESENCE_UTIL_H_
+
+namespace content {
+class BrowserContext;
+}
+
+namespace copresence {
+class CopresenceClient;
+class WhispernetClient;
+}
+
+namespace extensions {
+
+class CopresenceService;
+

[not at google - send to devlin, 2014/08/07 20:41:18]

these utils have a pretty small value, and it seems like they're basically used
in copresence_api.cc only. just put them in there, if really necessary?

[rkc, 2014/08/07 21:43:02]

They're used from copresence_private_api.cc, otherwise I'd have put them only in
copresence_api.cc

[not at google - send to devlin, 2014/08/07 21:47:43]

they're such low value though. A null check? It's hardly worth creating a whole
util system for. it's another file I went and had a look at, and anybody else
reading this API will need to check it out as well. just added complexity for no
gain.

[rkc, 2014/08/07 22:03:45]

Agreed, it isn't really a big benefit. Removed.
Done.

+CopresenceService* GetCopresenceService(
+    content::BrowserContext* browser_context);
+
+copresence::CopresenceClient* GetCopresenceClient(
+    content::BrowserContext* browser_context);
+
+copresence::WhispernetClient* GetWhispernetClient(
+    content::BrowserContext* browser_context);
+
+}  // namespace extensions
+
+#endif  // CHROME_BROWSER_EXTENSIONS_API_COPRESENCE_COPRESENCE_UTIL_H_