Update from https://crrev.com/329939

base/prefs/writeable_pref_store.h

Index: base/prefs/writeable_pref_store.h
diff --git a/base/prefs/writeable_pref_store.h b/base/prefs/writeable_pref_store.h
index 5ebab6428235015fdf8e5f29f8bd6311bd0da56c..d85b4c8d4272a054889e2b8eb3c9fe94292ec262 100644
--- a/base/prefs/writeable_pref_store.h
+++ b/base/prefs/writeable_pref_store.h
@@ -17,14 +17,27 @@ class Value;
 // A pref store that can be written to as well as read from.
 class BASE_PREFS_EXPORT WriteablePrefStore : public PrefStore {
  public:
+  // PrefWriteFlags can be used to change the way a pref will be written to
+  // storage.
+  enum PrefWriteFlags : uint32 {
+    // No flags are specified.
+    DEFAULT_PREF_WRITE_FLAGS = 0,
+
+    // This marks the pref as "lossy". There is no strict time guarantee on when
+    // a lossy pref will be persisted to permanent storage when it is modified.
+    LOSSY_PREF_WRITE_FLAG = 1 << 1
+  };
+
   WriteablePrefStore() {}
 
   // Sets a |value| for |key| in the store. Assumes ownership of |value|, which
-  // must be non-NULL.
-  virtual void SetValue(const std::string& key, base::Value* value) = 0;
+  // must be non-NULL. |flags| is a bitmask of PrefWriteFlags.
+  virtual void SetValue(const std::string& key,
+                        base::Value* value,
+                        uint32 flags) = 0;
 
   // Removes the value for |key|.
-  virtual void RemoveValue(const std::string& key) = 0;
+  virtual void RemoveValue(const std::string& key, uint32 flags) = 0;
 
   // Equivalent to PrefStore::GetValue but returns a mutable value.
   virtual bool GetMutableValue(const std::string& key,
@@ -34,13 +47,17 @@ class BASE_PREFS_EXPORT WriteablePrefStore : public PrefStore {
   // if one retrieves a list or dictionary with GetMutableValue and change its
   // value. SetValue takes care of notifications itself. Note that
   // ReportValueChanged will trigger notifications even if nothing has changed.
-  virtual void ReportValueChanged(const std::string& key) = 0;
+  // |flags| is a bitmask of PrefWriteFlags.
+  virtual void ReportValueChanged(const std::string& key, uint32 flags) = 0;
 
   // Same as SetValue, but doesn't generate notifications. This is used by
   // PrefService::GetMutableUserPref() in order to put empty entries
   // into the user pref store. Using SetValue is not an option since existing
-  // tests rely on the number of notifications generated.
-  virtual void SetValueSilently(const std::string& key, base::Value* value) = 0;
+  // tests rely on the number of notifications generated. |flags| is a bitmask
+  // of PrefWriteFlags.
+  virtual void SetValueSilently(const std::string& key,
+                                base::Value* value,
+                                uint32 flags) = 0;
 
  protected:
   ~WriteablePrefStore() override {}