Remove a bunch of DeepCopy() calls in the chrome.storage API.

chrome/browser/extensions/api/storage/setting_sync_data.h

 // Copyright (c) 2012 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_STORAGE_SETTING_SYNC_DATA_H_
 #define CHROME_BROWSER_EXTENSIONS_API_STORAGE_SETTING_SYNC_DATA_H_
 
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/values.h"
@@ skipping 33 matching lines @@
 
   // Returns the extension id the setting is for.
   const std::string& extension_id() const;
 
   // Returns the settings key.
   const std::string& key() const;
 
   // Returns the value of the setting.
   const base::Value& value() const;
 
+  // Releases ownership of the value to the caller.
+  //
+  // Be careful when calling this, as SettingSyncData is effectively a

[Devlin, 2015/05/15 21:59:07]

Hmm...

Generally, it's best to avoid saying "Be careful, because it's really easy to
shoot yourself in the foot with this."

Without looking into this too much, it seems possible to make SettingSyncData
DISALLOW_COPY_AND_ASSIGN, since we could use a ScopedVector for
SettingSyncDataList.  But I haven't delved deep enough to know if we could... is
there a hard blocker preventing that?

[not at google - send to devlin, 2015/05/15 23:28:30]

The blocker is this diff blowing up even more, but done. Simplified some code,
complicated some tests. Win?

[Devlin, 2015/05/15 23:58:18]

Win.

+  // refcounted wrapper around internal state, which can be shared between
+  // multiple SettingSyncData instances.
+  //
+  // Therefore, releasing the value may unexpectedly release the value from
+  // other SettingSyncData instances.
+  scoped_ptr<base::Value> PassValue();
+
  private:
   // Ref-counted container for the data.
   // TODO(kalman): Use browser_sync::Immutable<Internal>.
   class Internal : public base::RefCountedThreadSafe<Internal> {
    public:
     Internal(
       syncer::SyncChange::SyncChangeType change_type,
       const std::string& extension_id,
       const std::string& key,
       scoped_ptr<base::Value> value);
@@ skipping 18 matching lines @@
       const sync_pb::ExtensionSettingSpecifics& specifics);
 
   scoped_refptr<Internal> internal_;
 };
 
 typedef std::vector<SettingSyncData> SettingSyncDataList;
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_API_STORAGE_SETTING_SYNC_DATA_H_