Adds support for multiple displays to WmTestBase

ash/mus/window_manager.cc

Index: ash/mus/window_manager.cc
diff --git a/ash/mus/window_manager.cc b/ash/mus/window_manager.cc
index 69a2992a7c08fb222113a7bf0d9fe96b2881f42e..eb9ce110142030f24df31d9fdf2abc3c17e80e1d 100644
--- a/ash/mus/window_manager.cc
+++ b/ash/mus/window_manager.cc
@@ -181,6 +181,21 @@ RootWindowController* WindowManager::CreateRootWindowController(
   return root_window_controller;
 }
 
+void WindowManager::RemoveDisplay(ui::Window* window) {

[msw, 2016/09/12 22:01:51]

q: just window->Destroy and let OnWindowDestroy[ing|ed] do the rest?
(I see you want to move away from that pattern, so maybe it's okay to support
both and leave this as-is for now... just more code!)

[sky, 2016/09/12 23:11:27]

Indeed. I want to move away from the observer and prefer this approach.

+  // TODO(sky): WindowManager shouldn't need to observer the windows. Instead

[msw, 2016/09/12 22:01:51]

nit: "observer"

[sky, 2016/09/12 23:11:27]

Done.

+  // WindowManager should have a specific API that is called when a display is
+  // removed.
+  auto it = FindRootWindowControllerByWindow(window);
+  DCHECK(it != root_window_controllers_.end());
+  FOR_EACH_OBSERVER(WindowManagerObserver, observers_,
+                    OnWillDestroyRootWindowController((*it).get()));
+  root_window_controllers_.erase(it);
+  // Remove the observer so we don't see the OnWindowDestroying/Destroyed as we
+  // already handled it here.
+  window->RemoveObserver(this);
+  window->Destroy();
+}
+
 void WindowManager::Shutdown() {
   if (!window_tree_client_)
     return;
@@ -206,28 +221,28 @@ void WindowManager::Shutdown() {
   window_manager_client_ = nullptr;
 }
 
-void WindowManager::OnWindowDestroying(ui::Window* window) {
+WindowManager::RootWindowControllers::iterator
+WindowManager::FindRootWindowControllerByWindow(ui::Window* window) {
   for (auto it = root_window_controllers_.begin();

[msw, 2016/09/12 22:01:51]

optional nit: for (auto it : root_window_controllers_) {

[sky, 2016/09/12 23:11:27]

That'll give me a std::unique_ptr<RootWindowController*>&. I want the iterator.

        it != root_window_controllers_.end(); ++it) {
-    if ((*it)->root() == window) {
-      FOR_EACH_OBSERVER(WindowManagerObserver, observers_,
-                        OnWillDestroyRootWindowController((*it).get()));
-      return;
-    }
+    if ((*it)->root() == window)
+      return it;
   }
-  NOTREACHED();
+  return root_window_controllers_.end();
+}
+
+void WindowManager::OnWindowDestroying(ui::Window* window) {
+  auto it = FindRootWindowControllerByWindow(window);
+  DCHECK(it != root_window_controllers_.end());
+  FOR_EACH_OBSERVER(WindowManagerObserver, observers_,
+                    OnWillDestroyRootWindowController((*it).get()));
 }
 
 void WindowManager::OnWindowDestroyed(ui::Window* window) {
+  auto it = FindRootWindowControllerByWindow(window);
+  DCHECK(it != root_window_controllers_.end());
   window->RemoveObserver(this);
-  for (auto it = root_window_controllers_.begin();
-       it != root_window_controllers_.end(); ++it) {
-    if ((*it)->root() == window) {
-      root_window_controllers_.erase(it);
-      return;
-    }
-  }
-  NOTREACHED();
+  root_window_controllers_.erase(it);
 }
 
 void WindowManager::OnEmbed(ui::Window* root) {