Makes it so each windowtreeclient can use whatever ids it wants

components/mus/ws/test_change_tracker.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "components/mus/ws/test_change_tracker.h"
 
 #include <stddef.h>
 
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
@@ skipping 131 matching lines @@
   std::string result;
   for (auto& change : changes) {
     if (!result.empty())
       result += "\n";
     result += ChangeToDescription1(change);
   }
   return result;
 }
 
 std::string SingleWindowDescription(const std::vector<TestWindow>& windows) {
-  if (windows.size() != 1u)
-    return "more than one changes and expected only one";
-  return windows[0].ToString();
+  if (windows.empty())
+    return "no windows";
+  std::string result;
+  for (const TestWindow& window : windows)
+    result += window.ToString();
+  return result;
 }
 
 std::string ChangeWindowDescription(const std::vector<Change>& changes) {
   if (changes.size() != 1)
     return std::string();
   std::vector<std::string> window_strings(changes[0].windows.size());
   for (size_t i = 0; i < changes[0].windows.size(); ++i)
     window_strings[i] = "[" + changes[0].windows[i].ToString() + "]";
   return base::JoinString(window_strings, ",");
 }
@@ skipping 223 matching lines @@
 std::string TestWindow::ToString2() const {
   return base::StringPrintf(
       "window=%s parent=%s visible=%s drawn=%s",
       WindowIdToString(window_id).c_str(), WindowIdToString(parent_id).c_str(),
       visible ? "true" : "false", drawn ? "true" : "false");
 }
 
 }  // namespace ws
 
 }  // namespace mus