try disabling 'blockSelectEvents' flag

Summary:
In the past Draft.js set a 'blockSelectEvents' flag on 'componentWillUpdate'
and unset it in 'componentDidUpdate'.

The reason for this, according to comments in the code, was that IE will fire
a 'selectionChange' event when we programmatically change the selection,
meaning it would trigger a new select event while we are in the middle of
updating.

**Edit:**
We found that the 'selection.addRange' was what triggered the stray `selectionchange` event in IE, for the record.[1] Thanks sophiebits for the tip about that.

When manually testing, I saw no bugs or inconsistencies introduced when the extra 'selectionchange' event fired in IE. The event would go into React, and yet it was never logged as triggering a handler in Draft.js.

So either that `selectionchange` event was not one that Draft.js. listened to, or React ignores/defers it because it's in the middle of a commit.

This diff does two things:
- Add logging to verify if we ever actually use the `blockSelectEvents` flag in practice. Is it actually blocking anything??? And if not, as I suspect, then;
- We can just remove it. This also removes it under a GK, so we can test on 50% employees first and see if they experience any bugs.

Lastly - I do want to add tests for this. It is error-prone and time consuming to set up and repeately do manual testing. Going to put together an outline of what I think the test should look like in a follow-up diff.

 ---
[1]: Here are the logs I recorded, for posterity
```
// inside of DraftEditor#focus
calling forceSelection
calling udpate with new editor state and new selection
componentWillUpdate fired!
This is where blockSelectEvents would be set to true~~~
a leaf is about to call setDraftEditorSelection
removing all ranges from the selection
calling range.setStart
**calling selection.addRange**
**React got an event of type topSelectionChange**
**window got an event of 'selectionchange'**
componentDidUpdate fired
This is where blockSelectEvents would be set to false~~~
React got an event of type topBlur
React got an event of type topFocus
Draft got an event of onFocus
Draft returned early because currentSelection already matches the updated selection
```

Reviewed By: sophiebits

Differential Revision: D6866079

fbshipit-source-id: 01034c6404df892224f5c18a45cba744a64d6e38

src/component/base/DraftEditor.react.js

@@ -378,7 +378,11 @@ class DraftEditor extends React.Component<DraftEditorProps, State> {
    * of browser interaction, not re-renders and forced selections.
    */
   componentWillUpdate(nextProps: DraftEditorProps): void {
-    this._blockSelectEvents = true;
+    if (!gkx('draft_js_stop_blocking_select_events')) {
+      // We suspect this is not actually needed with modern React
+      // For people in the GK, we will skip setting this flag.
+      this._blockSelectEvents = true;
+    }
     this._latestEditorState = nextProps.editorState;
   }
 
@@ -414,6 +418,7 @@ class DraftEditor extends React.Component<DraftEditorProps, State> {
       editorNode instanceof HTMLElement,
       'editorNode is not an HTMLElement',
     );
+
     editorNode.focus();
 
     // Restore scroll position

src/component/handlers/edit/editOnSelect.js

@@ -15,6 +15,7 @@
 
 import type DraftEditor from 'DraftEditor.react';
 
+const DraftJsDebugLogging = require('DraftJsDebugLogging');
 var EditorState = require('EditorState');
 var ReactDOM = require('ReactDOM');
 
@@ -26,6 +27,16 @@ function editOnSelect(editor: DraftEditor): void {
     editor._blockSelectEvents ||
     editor._latestEditorState !== editor.props.editorState
   ) {
+    if (editor._blockSelectEvents) {
+      const editorState = editor.props.editorState;
+      const selectionState = editorState.getSelection();
+      DraftJsDebugLogging.logBlockedSelectionEvent({
+        // For now I don't think we need any other info
+        anonymizedDom: 'N/A',
+        extraParams: '',
+        selectionState: JSON.stringify(selectionState.toJS()),
+      });
+    }
     return;
   }
 

src/stubs/DraftJsDebugLogging.js

@@ -12,5 +12,6 @@
 'use strict';
 
 module.exports = {
+  logBlockedSelectionEvent: () => null,
   logSelectionStateFailure: () => null,
 };