Remove special DataTransfer permissions for file: origins.

third_party/WebKit/LayoutTests/fast/dnd/resources/copy-data-transfer.js

+// Copies the information out of a DataTransfer instance. This is necessary
+// because dataTransfer instances get neutered after their event handlers exit.
+//
+// Returns a Promise that resolves to an object which mirrors the DataTransfer's
+// files, items, and types attributes, as well as the return values of the
+// getData function.
+const copyDataTransfer = (dataTransfer) => {
+  const types = dataTransfer.types.slice();
+  const data = {};
+  for (let type of types) {
+    try {
+      data[type] = dataTransfer.getData(type);
+    } catch(e) {  // Catches SecurityError exceptions.
+      data[type] = e;
+    }
+  }
+
+  const readerPromises = [];
+
+  // DataTransfer.files returns a FileList. According to the spec, FileList only
+  // supports .length and .item().
+  const files = [];
+  const fileList = dataTransfer.files || [];
+  for (let i = 0; i < fileList.length; ++i) {
+    const file = fileList.item(i);
+    const fileData = { file: file };
+    files.push(fileData);
+
+    readerPromises.push(new Promise((resolve, reject) => {
+      const reader = new FileReader();
+      reader.onloadend = (event) => {
+        if (event.target.error)
+          fileData.data = event.target.error;
+        else
+          fileData.data = event.target.result;
+        resolve();
+      };
+      reader.readAsText(file);
+    }).catch(e => fileData.error = e));
+  }
+
+  // DataTransfer.items returns an DataTransferItemList, which supports .length
+  // and indexed access.
+  const items = [];
+  const itemList = dataTransfer.items || [];
+  for (let i = 0; i < dataTransfer.items.length; ++i) {
+    const item = dataTransfer.items[i];
+    const itemData = { kind: item.kind, type: item.type };
+    items.push(itemData);
+
+    readerPromises.push(new Promise((resolve, reject) => {
+      if (itemData.kind === 'file') {
+        itemData.file = item.getAsFile();
+        if (itemData.file === null) {  // DataTransfer is in protected mode.
+          resolve();
+          return;
+        }
+
+        const reader = new FileReader();
+        reader.onloadend = (event) => {
+          if (event.target.error)
+            itemData.data = event.target.error;
+          else
+            itemData.data = event.target.result;
+          resolve();
+        };
+        reader.readAsText(itemData.file);
+      }
+    }).catch(e => itemData.error = e));
+  }
+
+  return Promise.all(readerPromises).then(() => {
+    return { data: data, files: files, items: items, types: types };
+  });
+};