Introduce ChromeZoomLevelPref, make zoom level prefs independent of profile prefs.

chrome/browser/profiles/profile.cc

Index: chrome/browser/profiles/profile.cc
diff --git a/chrome/browser/profiles/profile.cc b/chrome/browser/profiles/profile.cc
index 86326aa08254a89069e62c9a11413e3bb6e9d9d3..ea8151dea669d8d71f05b44524ca73e7b81a1ca8 100644
--- a/chrome/browser/profiles/profile.cc
+++ b/chrome/browser/profiles/profile.cc
@@ -60,6 +60,10 @@ TestingProfile* Profile::AsTestingProfile() {
   return NULL;
 }
 
+chrome::ChromeZoomLevelPrefs* Profile::GetZoomLevelPrefs() {
+  return NULL;
+}
+
 Profile::Delegate::~Delegate() {
 }
 
@@ -136,11 +140,20 @@ void Profile::RegisterProfilePrefs(user_prefs::PrefRegistrySyncable* registry) {
       prefs::kSelectFileLastDirectory,
       std::string(),
       user_prefs::PrefRegistrySyncable::UNSYNCABLE_PREF);
+  // TODO(wjmaclean): remove the following two prefs once migration to per-
+  // partition zoom is complete.
   registry->RegisterDoublePref(
-      prefs::kDefaultZoomLevel,
+      prefs::kDefaultZoomLevelInProfile,
       0.0,
       user_prefs::PrefRegistrySyncable::UNSYNCABLE_PREF);
   registry->RegisterDictionaryPref(
+      prefs::kPerHostZoomLevelsInProfile,
+      user_prefs::PrefRegistrySyncable::UNSYNCABLE_PREF);
+
+  registry->RegisterDictionaryPref(
+      prefs::kDefaultZoomLevel,

[battre, 2014/10/06 14:33:51]

This looks like pretty perilous: You are changing the type of kDefualtZoomLevel.
Please don't do that.

I suggest to rename kDefaultZoomLevel to kDefaultZoomLevelDeprecated, introduce
a *new* kPartitionDefaultZoomLevel, and then add a TODO to rename
kPartitionDefaultZoomLevel to kDefaultZoomLevels later.

[wjmaclean, 2014/10/06 16:58:12]

Done.

Might it be useful to just leave it as kPartitionDefaultZoomLevel, to remind
people that it's per-partition?

[battre, 2014/10/08 11:27:10]

Acknowledged.

+      user_prefs::PrefRegistrySyncable::UNSYNCABLE_PREF);
+  registry->RegisterDictionaryPref(
       prefs::kPerHostZoomLevels,
       user_prefs::PrefRegistrySyncable::UNSYNCABLE_PREF);
   registry->RegisterStringPref(