DevTools: Assign proper distances to non user reachable objects.

Do not assign zero distance to all GC root objects.
Instead assign zero to the global root and follow strong roots only
from there.

BUG=906847

Change-Id: Iee22162ac11a6700e019276daee1357ef33e61b9
Reviewed-on: https://chromium-review.googlesource.com/c/1353995
Commit-Queue: Alexei Filippov <alph@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612438}

third_party/blink/renderer/devtools/front_end/heap_snapshot_worker/HeapSnapshot.js

@@ -1281,18 +1281,6 @@ HeapSnapshotWorker.HeapSnapshot = class {
     return true;
   }
 
-  /**
-   * @param {function(!HeapSnapshotWorker.HeapSnapshotNode)} action
-   * @param {boolean=} userRootsOnly
-   */
-  forEachRoot(action, userRootsOnly) {
-    for (let iter = this.rootNode().edges(); iter.hasNext(); iter.next()) {
-      const node = iter.edge.node();
-      if (!userRootsOnly || this.isUserRoot(node))
-        action(node);
-    }
-  }
-
   /**
    * @param {function(!HeapSnapshotWorker.HeapSnapshotNode,!HeapSnapshotWorker.HeapSnapshotEdge):boolean=} filter
    */
@@ -1306,24 +1294,20 @@ HeapSnapshotWorker.HeapSnapshot = class {
     const nodesToVisit = new Uint32Array(this.nodeCount);
     let nodesToVisitLength = 0;
 
-    /**
-     * @param {number} distance
-     * @param {!HeapSnapshotWorker.HeapSnapshotNode} node
-     */
-    function enqueueNode(distance, node) {
-      const ordinal = node.ordinal();
-      if (distances[ordinal] !== noDistance)
-        return;
-      distances[ordinal] = distance;
-      nodesToVisit[nodesToVisitLength++] = node.nodeIndex;
+    // BFS for user root objects.
+    for (let iter = this.rootNode().edges(); iter.hasNext(); iter.next()) {
+      const node = iter.edge.node();
+      if (this.isUserRoot(node)) {
+        distances[node.ordinal()] = 1;
+        nodesToVisit[nodesToVisitLength++] = node.nodeIndex;
+      }
     }
-
-    this.forEachRoot(enqueueNode.bind(null, 1), true);
     this._bfs(nodesToVisit, nodesToVisitLength, distances, filter);
 
-    // bfs for the rest of objects
-    nodesToVisitLength = 0;
-    this.forEachRoot(enqueueNode.bind(null, HeapSnapshotModel.baseSystemDistance), false);
+    // BFS for objects not reached from user roots.
+    distances[this.rootNode().ordinal()] = HeapSnapshotModel.baseSystemDistance;
+    nodesToVisit[0] = this.rootNode().nodeIndex;
+    nodesToVisitLength = 1;
     this._bfs(nodesToVisit, nodesToVisitLength, distances, filter);
   }
 
@@ -2581,60 +2565,6 @@ HeapSnapshotWorker.JSHeapSnapshot = class extends HeapSnapshotWorker.HeapSnapsho
     return node.isUserRoot() || node.isDocumentDOMTreesRoot();
   }
 
-  /**
-   * @override
-   * @param {function(!HeapSnapshotWorker.HeapSnapshotNode)} action
-   * @param {boolean=} userRootsOnly
-   */
-  forEachRoot(action, userRootsOnly) {
-    /**
-     * @param {!HeapSnapshotWorker.HeapSnapshotNode} node
-     * @param {string} name
-     * @return {?HeapSnapshotWorker.HeapSnapshotNode}
-     */
-    function getChildNodeByName(node, name) {
-      for (let iter = node.edges(); iter.hasNext(); iter.next()) {
-        const child = iter.edge.node();
-        if (child.name() === name)
-          return child;
-      }
-      return null;
-    }
-
-    const visitedNodes = {};
-    /**
-     * @param {!HeapSnapshotWorker.HeapSnapshotNode} node
-     */
-    function doAction(node) {
-      const ordinal = node.ordinal();
-      if (!visitedNodes[ordinal]) {
-        action(node);
-        visitedNodes[ordinal] = true;
-      }
-    }
-
-    const gcRoots = getChildNodeByName(this.rootNode(), '(GC roots)');
-    if (!gcRoots)
-      return;
-
-    if (userRootsOnly) {
-      for (let iter = this.rootNode().edges(); iter.hasNext(); iter.next()) {
-        const node = iter.edge.node();
-        if (this.isUserRoot(node))
-          doAction(node);
-      }
-    } else {
-      for (let iter = gcRoots.edges(); iter.hasNext(); iter.next()) {
-        const subRoot = iter.edge.node();
-        for (let iter2 = subRoot.edges(); iter2.hasNext(); iter2.next())
-          doAction(iter2.edge.node());
-        doAction(subRoot);
-      }
-      for (let iter = this.rootNode().edges(); iter.hasNext(); iter.next())
-        doAction(iter.edge.node());
-    }
-  }
-
   /**
    * @override
    * @return {?{map: !Uint32Array, flag: number}}

third_party/blink/web_tests/inspector-protocol/heap-profiler/heap-snapshot-merged-nodes-expected.txt

@@ -2,5 +2,5 @@ Test that DOM node and its JS wrapper appear as a single node.
 Took heap snapshot
 Parsed snapshot
 SUCCESS: found leaking
-SUCCESS: retaining path = [Detached V8EventListener, Detached EventListener, Detached InternalNode, Detached InternalNode, Detached HTMLDivElement, Window / file://, ]
+SUCCESS: retaining path = [Detached V8EventListener, Detached EventListener, Detached InternalNode, Detached InternalNode, Detached HTMLDivElement, Window / file://]
 

third_party/blink/web_tests/inspector-protocol/heap-profiler/heap-snapshot-with-event-listener-expected.txt

@@ -2,5 +2,5 @@ Test retaining path for an event listener.
 Took heap snapshot
 Parsed snapshot
 SUCCESS: found myEventListener
-SUCCESS: retaining path = [V8EventListener, EventListener, InternalNode, InternalNode, HTMLBodyElement, HTMLHtmlElement, HTMLDocument, Window / file://, ]
+SUCCESS: retaining path = [V8EventListener, EventListener, InternalNode, InternalNode, HTMLBodyElement, HTMLHtmlElement, HTMLDocument, Window / file://]
 

third_party/blink/web_tests/inspector-protocol/heap-profiler/heap-snapshot-with-multiple-retainers-expected.txt

@@ -6,6 +6,6 @@ SUCCESS: immediate retainer is V8EventListener.
 SUCCESS: immediate retainer is EventListener.
 SUCCESS: found single retaining path for v8EventListener.
 SUCCESS: found multiple retaining paths.
-SUCCESS: path1 = [InternalNode, HTMLBodyElement, HTMLHtmlElement, HTMLDocument, Window / file://, ]
-SUCCESS: path2 = [InternalNode, HTMLDivElement, HTMLBodyElement, HTMLHtmlElement, HTMLDocument, Window / file://, ]
+SUCCESS: path1 = [InternalNode, HTMLBodyElement, HTMLHtmlElement, HTMLDocument, Window / file://]
+SUCCESS: path2 = [InternalNode, HTMLDivElement, HTMLBodyElement, HTMLHtmlElement, HTMLDocument, Window / file://]