Bug 1486364 - Revert changes in Tree component and test; r=jdescottes.

In https://github.com/devtools-html/debugger.html/pull/6809 a check
was removed in the Tree component because seens as unnecessary, and
a test was modified to accomodate the change. Turns out the test was
needed in its original form, and was surfacing a bug.
This patch rolls back both the change in the Tree component _and_ in
the test.
The Tree modification will be backported to the Github repository.

Differential Revision: https://phabricator.services.mozilla.com/D4307

--HG--
extra : moz-landing-system : lando

devtools/client/shared/components/reps/reps.js

@@ -4465,7 +4465,17 @@ class Tree extends Component {
         if (focused || !nativeEvent || !this.treeRef) {
           return;
         }
-        this._focus(traversal[0].item);
+
+        const { explicitOriginalTarget } = nativeEvent;
+        // Only set default focus to the first tree node if the focus came
+        // from outside the tree (e.g. by tabbing to the tree from other
+        // external elements).
+        if (
+          explicitOriginalTarget !== this.treeRef &&
+          !this.treeRef.contains(explicitOriginalTarget)
+        ) {
+          this._focus(traversal[0].item);
+        }
       },
       onBlur: this._onBlur,
       "aria-label": this.props.label,

devtools/client/webconsole/test/mochitest/browser_webconsole_object_inspector_scroll.js

@@ -39,7 +39,8 @@ add_task(async function() {
   });
 
   info("Expand the last node");
-  lastNode.click();
+  const view = lastNode.ownerDocument.defaultView;
+  EventUtils.synthesizeMouseAtCenter(lastNode, {}, view);
   await onOiMutation;
 
   is(scrollTop, outputContainer.scrollTop,