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

chrome/browser/profiles/profile_impl.cc

Index: chrome/browser/profiles/profile_impl.cc
diff --git a/chrome/browser/profiles/profile_impl.cc b/chrome/browser/profiles/profile_impl.cc
index 5219a9f25616d7d31b1c2fa1a90d2e7ccc3e8459..55af26fc8ee3e2f1bf5c8a23ad0e4955a18eacd6 100644
--- a/chrome/browser/profiles/profile_impl.cc
+++ b/chrome/browser/profiles/profile_impl.cc
@@ -73,6 +73,7 @@
 #include "chrome/browser/ssl/chrome_ssl_host_state_delegate.h"
 #include "chrome/browser/ssl/chrome_ssl_host_state_delegate_factory.h"
 #include "chrome/browser/ui/startup/startup_browser_creator.h"
+#include "chrome/browser/ui/zoom/chrome_zoom_level_prefs.h"
 #include "chrome/common/chrome_constants.h"
 #include "chrome/common/chrome_paths_internal.h"
 #include "chrome/common/chrome_switches.h"
@@ -521,10 +522,6 @@ void ProfileImpl::DoFinalInit() {
       prefs::kSupervisedUserId,
       base::Bind(&ProfileImpl::UpdateProfileSupervisedUserIdCache,
                  base::Unretained(this)));
-  pref_change_registrar_.Add(
-      prefs::kDefaultZoomLevel,
-      base::Bind(&ProfileImpl::OnDefaultZoomLevelChanged,
-                 base::Unretained(this)));
 
   // Changes in the profile avatar.
   pref_change_registrar_.Add(
@@ -753,14 +750,46 @@ void ProfileImpl::DoFinalInit() {
 
 void ProfileImpl::InitHostZoomMap() {
   HostZoomMap* host_zoom_map = HostZoomMap::GetDefaultForBrowserContext(this);
-  host_zoom_map->SetDefaultZoomLevel(
-      prefs_->GetDouble(prefs::kDefaultZoomLevel));
+  // As part of the migration from per-profile to per-partition HostZoomMaps,
+  // we need to detect if an existing per-profile set of preferences exist, and
+  // if so convert them to be per-partition. We migrate any per-profile zoom
+  // level prefs via zoom_level_prefs_.
+  // Code that updates zoom prefs in the profile prefs store has been removed,
+  // so once we clear these values here, they should never get set again.
+  // TODO(wjmaclean): Remove this migration machinery several milestones after
+  // it goes stable. This means removing this entire function.
+  DCHECK(!zoom_level_prefs_);
+  zoom_level_prefs_.reset(
+      new chrome::ChromeZoomLevelPrefs(prefs_.get(), GetPath()));
+  zoom_level_prefs_->InitPrefsAndCopyToHostZoomMap(GetPath(),
+                                                         host_zoom_map);
+
+  // Only migrate the default zoom level if it is not equal to the registered
+  // default for the preference.
+  double default_default_zoom_level = 0.0;
+  prefs_->GetDefaultPrefValue(prefs::kProfileDefaultZoomLevel)
+      ->GetAsDouble(&default_default_zoom_level);
+  double per_profile_default_zoom_level =
+      prefs_->GetDouble(prefs::kProfileDefaultZoomLevel);
+  if (per_profile_default_zoom_level != default_default_zoom_level) {
+    // We cannot un-register this pref name, but we can reset it to a
+    // default sentinel value.
+    prefs_->SetDouble(prefs::kProfileDefaultZoomLevel,
+                      default_default_zoom_level);
+    zoom_level_prefs_->SetDefaultZoomLevelPref(
+        per_profile_default_zoom_level);
+  }
 
   const base::DictionaryValue* host_zoom_dictionary =
-      prefs_->GetDictionary(prefs::kPerHostZoomLevels);
+      prefs_->GetDictionary(prefs::kProfilePerHostZoomLevels);
   // Careful: The returned value could be NULL if the pref has never been set.
   if (host_zoom_dictionary != NULL) {
-    std::vector<std::string> keys_to_remove;
+    // Collect stats on frequency with which migrations are occuring.
+    if (!host_zoom_dictionary->empty()) {
+      content::RecordAction(
+          UserMetricsAction("Chrome_ZoomLevelPreferencesMigration"));

[Alexei Svitkine (slow), 2014/10/02 20:40:20]

I'm not convinced a user action is the best way to measure this.

For one, you don't have a baseline (just an absolute number - but you can't
answer questions such as what percentage of starts have migration).

Instead, I suggest using an enumerated histograms and recording both migrated
and non-migrated cases. That way, in addition to the total volume of these, you
can see how frequently it happens (i.e. vs. the non-migrated case).

Plus, histograms are better supported by our dashboards, so you can filter them
by different criteria, for example.

[wjmaclean, 2014/10/03 18:53:23]

Done.

[wjmaclean, 2014/10/03 18:53:23]

Done.

+    }
+
     for (base::DictionaryValue::Iterator i(*host_zoom_dictionary); !i.IsAtEnd();
          i.Advance()) {
       const std::string& host(i.key());
@@ -779,23 +808,21 @@ void ProfileImpl::InitHostZoomMap() {
       if (host.empty() ||
           content::ZoomValuesEqual(zoom_level,
                                    host_zoom_map->GetDefaultZoomLevel())) {
-        keys_to_remove.push_back(host);
         continue;
       }
 
+      // We push the profile per-host levels in through the HostZoomMap
+      // directly, which will update the zoom_level_prefs_ indirectly
+      // through the subsequent ZoomLevelChanged events.
       host_zoom_map->SetZoomLevelForHost(host, zoom_level);
     }
 
-    DictionaryPrefUpdate update(prefs_.get(), prefs::kPerHostZoomLevels);
-    base::DictionaryValue* host_zoom_dictionary = update.Get();
-    for (std::vector<std::string>::const_iterator it = keys_to_remove.begin();
-         it != keys_to_remove.end(); ++it) {
-      host_zoom_dictionary->RemoveWithoutPathExpansion(*it, NULL);
-    }
+    // We're done migrating the profile per-host zoom level values, so we clear
+    // them all.
+    DictionaryPrefUpdate update(prefs_.get(), prefs::kProfilePerHostZoomLevels);
+    base::DictionaryValue* host_zoom_dictionary_update = update.Get();
+    host_zoom_dictionary_update->Clear();
   }
-
-  zoom_subscription_ = host_zoom_map->AddZoomLevelChangedCallback(
-      base::Bind(&ProfileImpl::OnZoomLevelChanged, base::Unretained(this)));
 }
 
 base::FilePath ProfileImpl::last_selected_directory() {
@@ -1016,6 +1043,10 @@ PrefService* ProfileImpl::GetPrefs() {
   return prefs_.get();
 }
 
+chrome::ChromeZoomLevelPrefs* ProfileImpl::GetZoomLevelPrefs() {
+  return zoom_level_prefs_.get();
+}
+
 PrefService* ProfileImpl::GetOffTheRecordPrefs() {
   DCHECK(prefs_);
   if (!otr_prefs_) {
@@ -1164,26 +1195,6 @@ history::TopSites* ProfileImpl::GetTopSitesWithoutCreating() {
   return top_sites_.get();
 }
 
-void ProfileImpl::OnDefaultZoomLevelChanged() {
-  HostZoomMap::GetDefaultForBrowserContext(this)->SetDefaultZoomLevel(
-      pref_change_registrar_.prefs()->GetDouble(prefs::kDefaultZoomLevel));
-}
-
-void ProfileImpl::OnZoomLevelChanged(
-    const HostZoomMap::ZoomLevelChange& change) {
-
-  if (change.mode != HostZoomMap::ZOOM_CHANGED_FOR_HOST)
-    return;
-  HostZoomMap* host_zoom_map = HostZoomMap::GetDefaultForBrowserContext(this);
-  double level = change.zoom_level;
-  DictionaryPrefUpdate update(prefs_.get(), prefs::kPerHostZoomLevels);
-  base::DictionaryValue* host_zoom_dictionary = update.Get();
-  if (content::ZoomValuesEqual(level, host_zoom_map->GetDefaultZoomLevel()))
-    host_zoom_dictionary->RemoveWithoutPathExpansion(change.host, NULL);
-  else
-    host_zoom_dictionary->SetDoubleWithoutPathExpansion(change.host, level);
-}
-
 #if defined(ENABLE_SESSION_SERVICE)
 void ProfileImpl::StopCreateSessionServiceTimer() {
   create_session_service_timer_.Stop();