DevTools: Don't label top level completions as from the first prototype

In an object like {abc: 123}, the property 'abc' was mistakenly labeled
as being from the Object prototype.

ScreenShot: https://i.imgur.com/bdIWNDt.png

Bug: none

Change-Id: I85aed6eaa6561afbc54f52115ec9bf539fd345eb
Reviewed-on: https://chromium-review.googlesource.com/c/1460180
Commit-Queue: Joel Einbinder <einbinder@chromium.org>
Reviewed-by: Erik Luo <luoe@chromium.org>
Cr-Commit-Position: refs/heads/master@{#630533}

third_party/blink/renderer/devtools/front_end/object_ui/JavaScriptAutocomplete.js

@@ -413,7 +413,8 @@ ObjectUI.JavaScriptAutocomplete = class {
 
             const group = {items: [], __proto__: null};
             try {
-              if (typeof o === 'object' && o.constructor && o.constructor.name)
+              if (typeof o === 'object' && Object.prototype.hasOwnProperty.call(o, 'constructor') && o.constructor &&
+                  o.constructor.name)
                 group.title = o.constructor.name;
             } catch (ee) {
               // we could break upon cross origin check.

third_party/blink/web_tests/http/tests/devtools/console-completions-expected.txt

@@ -3,7 +3,6 @@ Tests completions prototype chain and scope variables.
 Completions for objectC.:
 {
     priority : 2
-    subtitle : "C"
     text : "instanceMember"
 }
 {
@@ -12,6 +11,7 @@ Completions for objectC.:
 }
 {
     priority : 3
+    subtitle : "C"
     text : "EPriorityMember"
 }
 {
@@ -39,7 +39,6 @@ Completions for objectC.:
 Completions for prefix:
 {
     priority : 4
-    subtitle : "Window"
     text : "prefixA"
 }
 {