Introduce enum InputType::ValueMode.

third_party/WebKit/Source/core/html/forms/BaseButtonInputType.cpp

Index: third_party/WebKit/Source/core/html/forms/BaseButtonInputType.cpp
diff --git a/third_party/WebKit/Source/core/html/forms/BaseButtonInputType.cpp b/third_party/WebKit/Source/core/html/forms/BaseButtonInputType.cpp
index 7485a3a8a9525147ea7fbd8ced3779b6af6c438a..269a0b18bc4df868e86644187aee5dc0a49599a7 100644
--- a/third_party/WebKit/Source/core/html/forms/BaseButtonInputType.cpp
+++ b/third_party/WebKit/Source/core/html/forms/BaseButtonInputType.cpp
@@ -81,8 +81,8 @@ LayoutObject* BaseButtonInputType::createLayoutObject(
   return new LayoutButton(&element());
 }
 
-bool BaseButtonInputType::storesValueSeparateFromAttribute() {
-  return false;
+InputType::ValueMode BaseButtonInputType::valueMode() const {
+  return ValueMode::kDefault;
 }
 
 void BaseButtonInputType::setValue(const String& sanitizedValue,