Let chrome_prefs handle Preferences initialization from master_preferences.

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 3449c31c9b4a2de4de7281e2bce8a118b1bf54c9..26c7c97257bcc0f3f76893f334952b70aede81e8 100644
--- a/chrome/browser/profiles/profile_impl.cc
+++ b/chrome/browser/profiles/profile_impl.cc
@@ -12,6 +12,7 @@
 #include "base/environment.h"
 #include "base/file_util.h"
 #include "base/files/file_path.h"
+#include "base/json/json_file_value_serializer.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/path_service.h"
 #include "base/prefs/json_pref_store.h"
@@ -419,7 +420,7 @@ void ProfileImpl::InitializePrefHashStoreIfRequired(
     const base::FilePath& profile_path) {
   scoped_ptr<PrefHashStoreImpl> pref_hash_store(GetPrefHashStore(profile_path));
   if (pref_hash_store && !pref_hash_store->IsInitialized()) {
-    chrome_prefs::InitializeHashStoreForPrefFile(
+    chrome_prefs::InitializeHashStoreFromPrefFile(
         GetPrefFilePathFromProfilePath(profile_path),
         JsonPrefStore::GetTaskRunnerForFile(
             profile_path, BrowserThread::GetBlockingPool()),
@@ -432,6 +433,35 @@ void ProfileImpl::ResetPrefHashStore(const base::FilePath& profile_path) {
   GetPrefHashStore(profile_path)->Reset();
 }
 
+// static
+bool ProfileImpl::InitializePrefsFromMasterPrefs(

[noms (inactive), 2014/02/04 20:36:35]

As discussed offline, these prefs related methods would probably live a better
life if they got moved out of profiles and into somewhere else like
chrome_prefs. The only Profile thing (other than the profile path) this method
needs is GetPrefHashStore, and that doesn't seem to actually need any Profile
specific things, (other than that path)

+    const base::FilePath& profile_path,
+    const base::DictionaryValue& master_prefs) {
+  // Create the profile directory if it doesn't exist yet (very possible on
+  // first run).
+  if (!base::CreateDirectory(profile_path))
+    return false;
+
+  JSONFileValueSerializer serializer(
+      GetPrefFilePathFromProfilePath(profile_path));
+
+  // Call Serialize (which does IO) on the main thread, which would _normally_
+  // be verboten. In this case however, we require this IO to synchronously
+  // complete before Chrome can start (as master preferences seed the Local
+  // State and Preferences files). This won't trip ThreadIORestrictions as they
+  // won't have kicked in yet on the main thread.
+  bool success = serializer.Serialize(master_prefs);
+
+  if (success) {
+    scoped_ptr<PrefHashStore> pref_hash_store(GetPrefHashStore(profile_path));
+    chrome_prefs::InitializeHashStoreFromMasterPrefs(master_prefs,
+                                                     pref_hash_store.Pass());
+  }
+
+  UMA_HISTOGRAM_BOOLEAN("Settings.InitializedFromMasterPrefs", success);
+  return success;
+}
+
 ProfileImpl::ProfileImpl(
     const base::FilePath& path,
     Delegate* delegate,