libchrome: add support for synchronous PropertySet::Set to dbus

dbus/property.h

Index: dbus/property.h
diff --git a/dbus/property.h b/dbus/property.h
index b308c8218a4d2cad8447bf7a93d74b336d556761..940ef715d86ba6656a063a99452d1544b58d5668 100644
--- a/dbus/property.h
+++ b/dbus/property.h
@@ -276,6 +276,8 @@ class CHROME_DBUS_EXPORT PropertySet {
   // depending on the remote object. This method may be overridden by
   // sub-classes if interfaces use different method calls.
   virtual void Set(PropertyBase* property, SetCallback callback);
+  // The sychronous version of Set().
+  virtual bool SetAndBlock(PropertyBase* property);
   virtual void OnSet(PropertyBase* property, SetCallback callback,
                      Response* response);
 
@@ -389,6 +391,12 @@ class CHROME_DBUS_EXPORT Property : public PropertyBase {
     property_set()->Set(this, callback);
   }
 
+  // The sychronous version of Set().
+  virtual bool SetAndBlock(const T& value) {
+    set_value_ = value;
+    return property_set()->SetAndBlock(this);
+  }
+
   // Method used by PropertySet to retrieve the value from a MessageReader,
   // no knowledge of the contained type is required, this method returns
   // true if its expected type was found, false if not.