Implement lossy pref behavior for JsonPrefStore.

base/prefs/json_pref_store.h

Index: base/prefs/json_pref_store.h
diff --git a/base/prefs/json_pref_store.h b/base/prefs/json_pref_store.h
index 2ad546da613df9386fdc6735c80761b2d399e3bb..ef260eb47da00b913918031bd55ed5b80978664a 100644
--- a/base/prefs/json_pref_store.h
+++ b/base/prefs/json_pref_store.h
@@ -29,6 +29,7 @@ class Clock;
 class DictionaryValue;
 class FilePath;
 class HistogramBase;
+class JsonPrefStoreLossyWriteTest;
 class SequencedTaskRunner;
 class SequencedWorkerPool;
 class Value;
@@ -165,6 +166,7 @@ class BASE_PREFS_EXPORT JsonPrefStore
                            WriteCountHistogramTestMultiplePeriods);
   FRIEND_TEST_ALL_PREFIXES(base::JsonPrefStoreTest,
                            WriteCountHistogramTestPeriodWithGaps);
+  friend class base::JsonPrefStoreLossyWriteTest;
 
   ~JsonPrefStore() override;
 
@@ -190,6 +192,10 @@ class BASE_PREFS_EXPORT JsonPrefStore
                         scoped_ptr<base::DictionaryValue> prefs,
                         bool schedule_write);
 
+  // Schedule a write with the file writer as long as |flags| doesn't contain
+  // WriteablePrefStore::LOSSY_PREF_WRITE_FLAG.
+  void ScheduleWrite(uint32 flags);
+
   const base::FilePath path_;
   const base::FilePath alternate_path_;
   const scoped_refptr<base::SequencedTaskRunner> sequenced_task_runner_;
@@ -208,6 +214,7 @@ class BASE_PREFS_EXPORT JsonPrefStore
 
   bool initialized_;
   bool filtering_in_progress_;
+  bool pending_lossy_write_;
   PrefReadError read_error_;
 
   std::set<std::string> keys_need_empty_value_;