Backed out changeset 3cea1d886e9e (bug 1238941) for being a possible cause of frequent devtools failures in browser_profiler_tree-abstract-02.js a=backout

--HG--
extra : commitid : 3MYM5fevzDQ

devtools/client/memory/components/dominator-tree.js

@@ -209,6 +209,9 @@ const DominatorTree = module.exports = createClass({
       getKey: node =>
         node instanceof DominatorTreeLazyChildren ? node.key() : node.nodeId,
       itemHeight: TREE_ROW_HEIGHT,
+      // We can't cache traversals because incremental fetching of children
+      // means the traversal might not be valid.
+      reuseCachedTraversal: _ => false,
     });
   }
 });

devtools/client/shared/components/tree.js

@@ -166,6 +166,10 @@ const Tree = module.exports = createClass({
     onFocus: PropTypes.func,
     // The depth to which we should automatically expand new items.
     autoExpandDepth: PropTypes.number,
+    // A predicate that returns true if the last DFS traversal that was cached
+    // can be reused, false otherwise. The predicate function is passed the
+    // cached traversal as an array of nodes.
+    reuseCachedTraversal: PropTypes.func,
     // Optional event handlers for when items are expanded or collapsed.
     onExpand: PropTypes.func,
     onCollapse: PropTypes.func,
@@ -174,6 +178,7 @@ const Tree = module.exports = createClass({
   getDefaultProps() {
     return {
       autoExpandDepth: AUTO_EXPAND_DEPTH,
+      reuseCachedTraversal: null,
     };
   },
 
@@ -182,6 +187,7 @@ const Tree = module.exports = createClass({
       scroll: 0,
       height: window.innerHeight,
       seen: new Set(),
+      cachedTraversal: undefined,
     };
   },
 
@@ -323,12 +329,23 @@ const Tree = module.exports = createClass({
    * Perform a pre-order depth-first search over the whole forest.
    */
   _dfsFromRoots(maxDepth = Infinity) {
-    const traversal = [];
+    const cached = this.state.cachedTraversal;
+    if (cached
+        && maxDepth === Infinity
+        && this.props.reuseCachedTraversal
+        && this.props.reuseCachedTraversal(cached)) {
+      return cached;
+    }
 
+    const traversal = [];
     for (let root of this.props.getRoots()) {
       this._dfs(root, maxDepth, traversal);
     }
 
+    if (this.props.reuseCachedTraversal) {
+      this.state.cachedTraversal = traversal;
+    }
+
     return traversal;
   },
 
@@ -348,6 +365,10 @@ const Tree = module.exports = createClass({
         }
       }
     }
+
+    this.setState({
+      cachedTraversal: null,
+    });
   }),
 
   /**
@@ -359,6 +380,10 @@ const Tree = module.exports = createClass({
     if (this.props.onCollapse) {
       this.props.onCollapse(item);
     }
+
+    this.setState({
+      cachedTraversal: null,
+    });
   }),
 
   /**