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

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

Index: chrome/browser/extensions/api/storage/setting_sync_data.h
diff --git a/chrome/browser/extensions/api/storage/setting_sync_data.h b/chrome/browser/extensions/api/storage/setting_sync_data.h
index 8fc0f91870307b233dd98c943eb1196e5ca5f21c..e4ce557f5223550c0069de957f7789444079ef6e 100644
--- a/chrome/browser/extensions/api/storage/setting_sync_data.h
+++ b/chrome/browser/extensions/api/storage/setting_sync_data.h
@@ -51,6 +51,16 @@ class SettingSyncData {
   // 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>.