Flow-type DataTransfer.js

Summary:
Flowifies DataTransfer.js. We have a flow libdef for the browser's DataTransfer object, **so the only non-flow change this involved was a quick name check to avoid the collision**.

This surfaced a couple of places where the module is misused (yay! means it's surfacing potential bugs!). Putting them behind flowfixme's to avoid changing functionality and keep this diff simple (and eye-testable).

I can make tasks for fixing these flowfixme's if desired.

Differential Revision: D16176363

fbshipit-source-id: 755da606d0d86b74f2024b6d8e522746072bfc61

Author: mrkev

src/component/handlers/drag/DraftEditorDragHandler.js

@@ -91,7 +91,9 @@ const DraftEditorDragHandler = {
       return;
     }
 
-    const files = data.getFiles();
+    /* $FlowFixMe This comment suppresses an error found DataTransfer was typed.
+     * getFiles() returns an array of <Files extends Blob>, not Blob */
+    const files: Array<Blob> = (data.getFiles(): any);
     if (files.length > 0) {
       if (
         editor.props.handleDroppedFiles &&
@@ -119,7 +121,11 @@ const DraftEditorDragHandler = {
       editor.update(moveText(editorState, dropSelection));
     } else {
       editor.update(
-        insertTextAtSelection(editorState, dropSelection, data.getText()),
+        insertTextAtSelection(
+          editorState,
+          dropSelection,
+          (data.getText(): any),
+        ),
       );
     }
     endDrag(editor);

src/component/handlers/edit/editOnPaste.js

@@ -37,7 +37,9 @@ function editOnPaste(editor: DraftEditor, e: SyntheticClipboardEvent<>): void {
 
   // Get files, unless this is likely to be a string the user wants inline.
   if (!data.isRichText()) {
-    const files = data.getFiles();
+    /* $FlowFixMe This comment suppresses an error found DataTransfer was typed.
+     * getFiles() returns an array of <Files extends Blob>, not Blob */
+    const files: Array<Blob> = (data.getFiles(): any);
     const defaultFileText = data.getText();
     if (files.length > 0) {
       // Allow customized paste handling for images, etc. Otherwise, fall
@@ -91,8 +93,8 @@ function editOnPaste(editor: DraftEditor, e: SyntheticClipboardEvent<>): void {
   }
 
   let textBlocks: Array<string> = [];
-  const text = data.getText();
-  const html = data.getHTML();
+  const text: string = (data.getText(): any);
+  const html: string = (data.getHTML(): any);
   const editorState = editor._latestEditorState;
 
   if (