DataTransfer: Make |types| be a FrozenArray<DOMString>.

third_party/WebKit/Source/core/clipboard/DataTransfer.cpp

Index: third_party/WebKit/Source/core/clipboard/DataTransfer.cpp
diff --git a/third_party/WebKit/Source/core/clipboard/DataTransfer.cpp b/third_party/WebKit/Source/core/clipboard/DataTransfer.cpp
index 2738516710bd335ed2df5c41eca8df85e30a864e..1941dce9a626612eb3b068f7d646f0b066ae59ff 100644
--- a/third_party/WebKit/Source/core/clipboard/DataTransfer.cpp
+++ b/third_party/WebKit/Source/core/clipboard/DataTransfer.cpp
@@ -168,10 +168,15 @@ void DataTransfer::clearData(const String& type) {
   if (!CanWriteData())
     return;
 
+  const size_t old_length = data_object_->length();
+
   if (type.IsNull())
     data_object_->ClearAll();
   else
     data_object_->ClearData(NormalizeType(type));
+
+  if (old_length != data_object_->length())
+    data_store_item_list_changed_ = true;
 }
 
 String DataTransfer::getData(const String& type) const {
@@ -190,9 +195,16 @@ void DataTransfer::setData(const String& type, const String& data) {
     return;
 
   data_object_->SetData(NormalizeType(type), data);
+  data_store_item_list_changed_ = true;
+}
+
+bool DataTransfer::hasDataStoreItemListChanged() {
+  if (!data_store_item_list_changed_)
+    return false;
+  data_store_item_list_changed_ = false;

[jsbell, 2017/05/12 17:07:35]

Hrm... most places where we use [CachedAttribute] the 
hasXXXChanged()/isXXXDirty() bool method is const and the flag/state is reset in
the xxx() accessor.

NavigatorLanguage is the only one like this. History and the 5 in the modules
are const methods. 

What do you think about changing this? i.e. make this method const, and move the
'... = false' line into types()

+  return true;
 }
 
-// extensions beyond IE's API
 Vector<String> DataTransfer::types() const {
   Vector<String> types;
   if (!CanReadTypes())
@@ -429,7 +441,8 @@ DataTransfer::DataTransfer(DataTransferType type,
       drop_effect_("uninitialized"),
       effect_allowed_("uninitialized"),
       transfer_type_(type),
-      data_object_(data_object) {}
+      data_object_(data_object),
+      data_store_item_list_changed_(true) {}
 
 void DataTransfer::setDragImage(ImageResourceContent* image,
                                 Node* node,