Factor Chrome details out of update manifest fetching.

extensions/browser/updater/default_manifest_fetch_data_delegate.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 EXTENSIONS_BROWSER_UPDATER_DEFAULT_MANIFEST_FETCH_DATA_DELEGATE_H_
+#define EXTENSIONS_BROWSER_UPDATER_DEFAULT_MANIFEST_FETCH_DATA_DELEGATE_H_
+
+#include "base/macros.h"
+#include "extensions/browser/updater/manifest_fetch_data_delegate.h"
+
+namespace extensions {
+
+class DefaultManifestFetchDataDelegate : public ManifestFetchDataDelegate {
+ public:
+  DefaultManifestFetchDataDelegate();
+  virtual ~DefaultManifestFetchDataDelegate();
+
+  // ManifestFetchDelegate implementation.
+  virtual std::string GetBaseQueryParams() OVERRIDE;
+  virtual bool ShouldAlwaysCheckWebstore() OVERRIDE;
+  virtual std::string GetBrandCode() OVERRIDE;

[not at google - send to devlin, 2014/08/12 16:33:02]

I guess that it's "nice", in some respects, to lump together providing
dependencies in the one place - but note that these 3 values are just static
data. You could just as easily pass them in as constructor parameters to
ManifestFetchData, and in fact, they do seem analogous to the |update_url|
parameter?

Another observation: ShouldAlwaysCheckWebstore is only called from
ExtensionDownloader, but that hasn't been moved to /extensions, so why the need
for the delegate there? What's wrong with it using
ChromeMetricsServiceAccessor::IsMetricsReportingEnabled?

So before I go on, here's an idea: make all of these constructor arguments to
ManifestFetchData. You may want to bundle them into a struct to avoid confusion,
maybe. WDYT?

+  virtual std::string GetPingParamsAndData(
+      const std::string& extension_id,
+      const ManifestFetchData::PingData& old_ping_data,
+      ManifestFetchData::PingData* new_ping_data) OVERRIDE;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(DefaultManifestFetchDataDelegate);
+};
+
+}  // namespace extensions
+
+#endif  // EXTENSIONS_BROWSER_UPDATER_DEFAULT_MANIFEST_FETCH_DATA_DELEGATE_H_