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..9cc4aa0ac28ce428c279e9d37aa87925b772ada2 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 {
@@ -190,14 +195,19 @@ 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() const {
+  return data_store_item_list_changed_ || !CanReadTypes();

[foolip, 2017/05/15 15:11:02]

Is there a test that would fail if the CanReadTypes() bit of this condition were
removed?

[Raphael Kubo da Costa (rakuco), 2017/05/15 15:17:59]

Yes; the previous iterations of this CL didn't have it, and were causing
SameSiteSubframe/DragAndDropBrowserTest.DragImageBetweenFrames/0 and 
CrossSiteSubframe/DragAndDropBrowserTest.DragImageBetweenFrames/0 (from
interactive_ui_tests) to fail because they were expecting "types" to return an
empty array on "dragend" events.

To be honest, I can't find anything on the spec saying types' behavior should
vary depending on the data store's mode but I found it safer to preserve that
part of the current behavior (ie. just because types returned a filled-in array
when the data store's mode was read-write doesn't mean the same array should be
returned when the data store's mode is set to "protected").

 }
 
-// extensions beyond IE's API
-Vector<String> DataTransfer::types() const {
+Vector<String> DataTransfer::types() {
   Vector<String> types;
   if (!CanReadTypes())
     return types;
 
+  data_store_item_list_changed_ = false;
   return data_object_->Types();
 }
 
@@ -429,7 +439,8 @@ 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,
@@ -461,7 +472,7 @@ bool DataTransfer::HasStringOfType(const String& type) const {
   if (!CanReadTypes())
     return false;
 
-  return types().Contains(type);
+  return data_object_->Types().Contains(type);
 }
 
 DragOperation ConvertDropZoneOperationToDragOperation(