DevTools: introduce object previews experiment

third_party/WebKit/Source/devtools/front_end/components/RemoteObjectPreviewFormatter.js

 // Copyright (c) 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 /**
  * @unrestricted
  */
 Components.RemoteObjectPreviewFormatter = class {
   /**
    * @param {!Protocol.Runtime.PropertyPreview} a
    * @param {!Protocol.Runtime.PropertyPreview} b
@@ skipping 10 matching lines @@
   /**
    * @param {!Element} parentElement
    * @param {!Protocol.Runtime.ObjectPreview} preview
    */
   appendObjectPreview(parentElement, preview) {
     var description = preview.description;
     if (preview.type !== 'object' || preview.subtype === 'null') {
       parentElement.appendChild(this.renderPropertyPreview(preview.type, preview.subtype, description));
       return;
     }
-    if (description && preview.subtype !== 'array')
-      parentElement.createTextChildren(description, ' ');
+    if (description) {
+      if (Runtime.experiments.isEnabled('objectPreviews')) {
+        var text = '';
+        if (preview.subtype === 'typedarray' || preview.subtype === 'map' || preview.subtype === 'set')
+          text = description.replace(/\[([0-9]+)\]|\(([0-9]+)\)/, '');

[dgozman, 2017/01/13 02:55:41]

- Why do we do this?
- Can description contains [5] because one of the elements is "[5]" ?

[luoe, 2017/01/13 23:20:12]

Motivation:
I want "arr = new Uint16Array([9])" to show up as "Uint16Array [9]" and not
Uint16Array(1) [9].  To do so, I take the raw description "Uint16Array(1)" and
remove the length/parens.

Array descriptions should not contain things like "[5]", unless the
internalConstructorName (constructor/class/inferred name) contains "[5]". 
Today, we are relying on this assumption in SDK.RemoteObject.arrayLength()'s
implementation.  I've moved this into RemoteObject.js, perhaps there is a better
place?

My intended behavior is:
typedarray
  name + size if>1
array
  size if>1
everything else
  description

I'm not sure if this is the right thing todo.  If you'd like something different
for the experiment, I'm open to change this.

+        else if (preview.subtype !== 'array')
+          text = description;
+        var size = SDK.RemoteObject.arrayLength(preview) || SDK.RemoteObject.mapOrSetEntriesCount(preview);
+        if (size > 1)
+          text += '(' + size + ')';
+        if (text.length > 0)
+          parentElement.createChild('span', 'object-description').textContent = text + ' ';
+      } else if (preview.subtype !== 'array') {
+        parentElement.createTextChildren(description, ' ');
+      }
+    }
 
     var isArray = preview.subtype === 'array' || preview.subtype === 'typedarray';
     parentElement.createTextChild(isArray ? '[' : '{');
     if (preview.entries)
       this._appendEntriesPreview(parentElement, preview);
     else if (isArray)
       this._appendArrayPropertiesPreview(parentElement, preview);
     else
       this._appendObjectPropertiesPreview(parentElement, preview);
     if (preview.overflow)
@@ skipping 182 matching lines @@
     if (type === 'object' && !subtype) {
       span.textContent = this._abbreviateFullQualifiedClassName(description);
       span.title = description;
       return span;
     }
 
     span.textContent = description;
     return span;
   }
 };