Improvements for debugger.html source tree

better30000.patch

diff --git a/src/components/PrimaryPanes/SourcesTree.js b/src/components/PrimaryPanes/SourcesTree.js
index eadd8041..79576b1e 100644
--- a/src/components/PrimaryPanes/SourcesTree.js
+++ b/src/components/PrimaryPanes/SourcesTree.js
@@ -242,7 +242,6 @@ class SourcesTree extends Component {
         onContextMenu={e => this.onContextMenu(e, item)}
       >
-        {arrow}
-        {icon}
+        {nodeHasChildren(item) ? arrow : null}
         <span className="label"> {item.name} </span>
       </div>
     );
diff --git a/src/utils/sources-tree/addToTree.js b/src/utils/sources-tree/addToTree.js
index c3ab0b11..1e514edf 100644
--- a/src/utils/sources-tree/addToTree.js
+++ b/src/utils/sources-tree/addToTree.js
@@ -15,7 +15,17 @@ import type { SourceRecord } from "../../reducers/types";
 function createNodeInTree(part: string, path: string, tree: Node) {
   const node = createNode(part, path, []);
   // we are modifying the tree
-  tree.contents = [...tree.contents, node];
+  const clone = tree.contents.slice(0);
+  clone.push(node);
+  tree.contents = clone;
+
+  let treeNameIndex = nodeNamesIndex.get(tree);
+  if (!treeNameIndex) {
+    treeNameIndex = Object.create(null);
+    nodeNamesIndex.set(tree, treeNameIndex);
+  }
+  treeNameIndex[part] = node;
+
   return node;
 }
 
@@ -33,7 +43,8 @@ function findOrCreateNode(
   index: number,
   url: Object
 ) {
-  const child = subTree.contents.find(c => c.name === part);
+  const namesIndex = nodeNamesIndex.get(subTree);
+  const child = namesIndex ? namesIndex[part] : undefined;
 
   // we create and enter the new node
   if (!child) {
@@ -116,3 +127,5 @@ export function addToTree(
   const finalNode = traverseTree(url, tree);
   finalNode.contents = addSourceToNode(finalNode, url, source);
 }
+
+let nodeNamesIndex = new WeakMap();
diff --git a/src/utils/sources-tree/sortTree.js b/src/utils/sources-tree/sortTree.js
index 48475aee..503c7aad 100644
--- a/src/utils/sources-tree/sortTree.js
+++ b/src/utils/sources-tree/sortTree.js
@@ -1,4 +1,19 @@
 import { nodeHasChildren, isExactUrlMatch } from "./utils";
+import { parse } from "url";
+
+function parseHost(debuggeeUrl) {
+  let { host } = parse(debuggeeUrl);
+  if (!host) {
+    return null;
+  }
+  return host.replace(/^www\./, "");
+}
+
+function isExactUrlMatch0(pathPart: string, debuggeeHost: string) {
+  return pathPart.indexOf("www.") === 0 ?
+      debuggeeHost === pathPart.substr(4) :
+      debuggeeHost === pathPart;
+}
 
 /**
  * Look at the nodes in the source tree, and determine the index of where to
@@ -7,9 +22,14 @@ import { nodeHasChildren, isExactUrlMatch } from "./utils";
  * @static
  */
 export function sortEntireTree(tree, debuggeeUrl = "") {
+  const debuggeeHost = parseHost(debuggeeUrl);
+  return sortEntireTree0(tree, debuggeeHost);
+}
+
+function sortEntireTree0(tree, debuggeeHost = null) {
   if (nodeHasChildren(tree)) {
-    const contents = sortTree(tree, debuggeeUrl).map(subtree =>
-      sortEntireTree(subtree)
+    const contents = sortTree0(tree, debuggeeHost).map(subtree =>
+      sortEntireTree0(subtree)
     );
     return { ...tree, contents };
   }
@@ -23,6 +43,11 @@ export function sortEntireTree(tree, debuggeeUrl = "") {
  * @static
  */
 export function sortTree(tree, debuggeeUrl = "") {
+  const debuggeeHost = parseHost(debuggeeUrl);
+  return sortTree0(debuggeeHost, debuggeeHost);
+}
+
+function sortTree0(tree, debuggeeHost) {
   return tree.contents.sort((previousNode, currentNode) => {
     const currentNodeIsDir = nodeHasChildren(currentNode);
     const previousNodeIsDir = nodeHasChildren(previousNode);
@@ -30,9 +55,9 @@ export function sortTree(tree, debuggeeUrl = "") {
       return 1;
     } else if (previousNode.name === "(index)") {
       return -1;
-    } else if (isExactUrlMatch(currentNode.name, debuggeeUrl)) {
+    } else if (debuggeeHost !== null && isExactUrlMatch0(currentNode.name, debuggeeHost)) {
       return 1;
-    } else if (isExactUrlMatch(previousNode.name, debuggeeUrl)) {
+    } else if (debuggeeHost !== null && isExactUrlMatch0(previousNode.name, debuggeeHost)) {
       return -1;
       // If neither is the case, continue to compare alphabetically
     } else if (previousNodeIsDir && !currentNodeIsDir) {