Add ability to change default pref values, and use in BrowserInstantController.

base/prefs/pref_registry.h

Index: base/prefs/pref_registry.h
diff --git a/base/prefs/pref_registry.h b/base/prefs/pref_registry.h
index 8f39341ce55b2fe9b43f78160e471c5d2a4b9e18..d8380eee28d2b056aafb9b43ba2cc1a219e7376e 100644
--- a/base/prefs/pref_registry.h
+++ b/base/prefs/pref_registry.h
@@ -15,7 +15,6 @@ class Value;
 }
 
 class DefaultPrefStore;
-class PrefStore;
 
 // Preferences need to be registered with a type and default value
 // before they are used.
@@ -34,11 +33,7 @@ class BASE_PREFS_EXPORT PrefRegistry : public base::RefCounted<PrefRegistry> {
   PrefRegistry();
 
   // Gets the registered defaults.
-  scoped_refptr<PrefStore> defaults();
-
-  // Allows iteration over defaults.
-  const_iterator begin() const;
-  const_iterator end() const;
+  scoped_refptr<DefaultPrefStore> defaults();

[Mattias Nissler (ping if slow), 2013/02/27 10:50:52]

I think we should rather not expose the DefaultPrefStore type here, but just add
a function to PrefRegistry:

void SetDefaultPrefValue(const char* pref_name, const Value* value);

That keeps the registration functions off limits, but still allows defaults to
be changed.

[Jói, 2013/02/27 16:30:56]

Done.

 
   // Exactly one callback can be set for registration. The callback
   // will be invoked each time registration has been performed on this