Fix a race condition in preference metric reporting.

base/prefs/json_pref_store.cc

Index: base/prefs/json_pref_store.cc
diff --git a/base/prefs/json_pref_store.cc b/base/prefs/json_pref_store.cc
index e230407043aea5ebc29056618ece54571e274b9c..e0391ff72bb8168bb49d7bcf148bae1d095a4116 100644
--- a/base/prefs/json_pref_store.cc
+++ b/base/prefs/json_pref_store.cc
@@ -13,6 +13,7 @@
 #include "base/json/json_string_value_serializer.h"
 #include "base/memory/ref_counted.h"
 #include "base/message_loop/message_loop_proxy.h"
+#include "base/prefs/pref_filter.h"
 #include "base/sequenced_task_runner.h"
 #include "base/threading/sequenced_worker_pool.h"
 #include "base/values.h"
@@ -151,12 +152,14 @@ scoped_refptr<base::SequencedTaskRunner> JsonPrefStore::GetTaskRunnerForFile(
 }
 
 JsonPrefStore::JsonPrefStore(const base::FilePath& filename,
-                             base::SequencedTaskRunner* sequenced_task_runner)
+                             base::SequencedTaskRunner* sequenced_task_runner,
+                             scoped_ptr<PrefFilter> pref_filter)
     : path_(filename),
       sequenced_task_runner_(sequenced_task_runner),
       prefs_(new base::DictionaryValue()),
       read_only_(false),
       writer_(filename, sequenced_task_runner),
+      pref_filter_(pref_filter.Pass()),
       initialized_(false),
       read_error_(PREF_READ_ERROR_OTHER) {}
 
@@ -268,7 +271,14 @@ void JsonPrefStore::CommitPendingWrite() {
 }
 
 void JsonPrefStore::ReportValueChanged(const std::string& key) {
-  FOR_EACH_OBSERVER(PrefStore::Observer, observers_, OnPrefValueChanged(key));
+  // Don't notify observers about changes during initialization (i.e., due to
+  // filters).
+  if (initialized_) {
+    if (pref_filter_.get())
+      pref_filter_->FilterUpdate(this, key);
+    FOR_EACH_OBSERVER(PrefStore::Observer, observers_, OnPrefValueChanged(key));
+  }
+
   if (!read_only_)
     writer_.ScheduleWrite(this);
 }
@@ -286,8 +296,6 @@ void JsonPrefStore::OnFileRead(base::Value* value_owned,
     return;
   }
 
-  initialized_ = true;
-
   switch (error) {
     case PREF_READ_ERROR_ACCESS_DENIED:
     case PREF_READ_ERROR_FILE_OTHER:
@@ -299,6 +307,8 @@ void JsonPrefStore::OnFileRead(base::Value* value_owned,
     case PREF_READ_ERROR_NONE:
       DCHECK(value.get());
       prefs_.reset(static_cast<base::DictionaryValue*>(value.release()));
+      if (pref_filter_.get())
+        pref_filter_->FilterOnLoad(this);
       break;
     case PREF_READ_ERROR_NO_FILE:
       // If the file just doesn't exist, maybe this is first run.  In any case
@@ -311,6 +321,8 @@ void JsonPrefStore::OnFileRead(base::Value* value_owned,
       NOTREACHED() << "Unknown error: " << error;
   }
 
+  initialized_ = true;
+
   if (error_delegate_.get() && error != PREF_READ_ERROR_NONE)
     error_delegate_->OnError(error);