DevTools: cleanup treeoutline expand logic

TreeElement.expand() should not need to check that the element has children and
TreeOutline.insertChild() should not automatically expand a child when it is
inserted. ObjectPropertiesSection.js depended on this logic to automatically
expand the Entries property. This CL updates it so that the Entries property is
added before expanded.

BUG=

Review-Url: https://codereview.chromium.org/2147343002
Cr-Commit-Position: refs/heads/master@{#407061}

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

@@ -584,11 +584,9 @@ WebInspector.ObjectPropertyTreeElement.populateWithProperties = function(treeNod
         for (var i = 0; i < internalProperties.length; i++) {
             internalProperties[i].parentObject = value;
             var treeElement = new WebInspector.ObjectPropertyTreeElement(internalProperties[i], linkifier);
-            if (internalProperties[i].name === "[[Entries]]") {
-                treeElement.setExpandable(true);
-                treeElement.expand();
-            }
             treeNode.appendChild(treeElement);
+            if (internalProperties[i].name === "[[Entries]]")
+                treeElement.expand();
         }
     }
     WebInspector.ObjectPropertyTreeElement._appendEmptyPlaceholderIfNeeded(treeNode, emptyPlaceholder);

third_party/WebKit/Source/devtools/front_end/ui/treeoutline.js

@@ -524,8 +524,6 @@ TreeElement.prototype = {
         this._childrenListNode.insertBefore(child._childrenListNode, nextSibling);
         if (child.selected)
             child.select();
-        if (child.expanded)
-            child.expand();
     },
 
     /**
@@ -883,7 +881,7 @@ TreeElement.prototype = {
 
     expand: function()
     {
-        if (!this._expandable || (this.expanded && this._children))
+        if (!this._expandable || this.expanded)
             return;
 
         // Set this before onpopulate. Since onpopulate can add elements, this makes