mus: Let clients set the cursor of their window.

components/mus/ws/event_dispatcher.cc

Index: components/mus/ws/event_dispatcher.cc
diff --git a/components/mus/ws/event_dispatcher.cc b/components/mus/ws/event_dispatcher.cc
index 384f9ba81f95b1c2d41d364a79a8a2653dabbe13..4cef2e2477ba66d218efeff02da8abd29c8c50d4 100644
--- a/components/mus/ws/event_dispatcher.cc
+++ b/components/mus/ws/event_dispatcher.cc
@@ -139,7 +139,10 @@ class EventMatcher {
 ////////////////////////////////////////////////////////////////////////////////
 
 EventDispatcher::EventDispatcher(EventDispatcherDelegate* delegate)
-    : delegate_(delegate), root_(nullptr) {}
+    : delegate_(delegate),
+      root_(nullptr),
+      mouse_button_down_(false),
+      mouse_cursor_source_window_(nullptr) {}
 
 EventDispatcher::~EventDispatcher() {
   std::set<ServerWindow*> pointer_targets;
@@ -215,6 +218,8 @@ void EventDispatcher::ProcessPointerEvent(mojom::EventPtr event) {
       pointer_target.window =
           FindDeepestVisibleWindowForEvents(root_, surface_id_, &location);
     }
+    if (!mouse_button_down_)
+      mouse_cursor_source_window_ = pointer_target.window;
     DispatchToPointerTarget(pointer_target, event.Pass());
     return;
   }
@@ -230,6 +235,9 @@ void EventDispatcher::ProcessPointerEvent(mojom::EventPtr event) {
     if (!IsObservingWindow(target))
       target->AddObserver(this);
 
+    mouse_button_down_ = true;

[sky, 2015/12/03 22:01:10]

This path is hit for both touch and mouse. Don't you only want to set these if
it's a mouse event?

[Elliot Glaysher, 2015/12/03 22:32:00]

Is it? In a previous comment you said this was only entered on first button
down, and that it was the other block that had to deal with touch.

Whatever. Put all access to mouse_cursor_source_window_ behind a variable that
checks POINTER_KIND_MOUSE.

+    mouse_cursor_source_window_ = target;
+
     pointer_targets_[pointer_id].window = target;
     pointer_targets_[pointer_id].in_nonclient_area =
         IsLocationInNonclientArea(target, location);
@@ -246,6 +254,20 @@ void EventDispatcher::ProcessPointerEvent(mojom::EventPtr event) {
       (event->pointer_data->kind != mojom::POINTER_KIND_MOUSE ||
        IsOnlyOneMouseButtonDown(event->flags));
 
+  if (should_reset_target &&
+      event->pointer_data &&
+      event->pointer_data->kind == mojom::PointerKind::POINTER_KIND_MOUSE) {
+    // When we release the mouse button, we want the cursor to be sourced from
+    // the window under the mouse pointer, even though we're sending the button
+    // up event to the window that had implicit capture. We have to set this
+    // before we perform dispatch because the Delegate is going to read this
+    // information from us.
+    mouse_button_down_ = false;
+    gfx::Point location(EventLocationToPoint(*event));
+    mouse_cursor_source_window_ =
+        FindDeepestVisibleWindowForEvents(root_, surface_id_, &location);
+  }
+
   DispatchToPointerTarget(pointer_targets_[pointer_id], event.Pass());
 
   if (should_reset_target) {
@@ -311,6 +333,9 @@ void EventDispatcher::OnWindowVisibilityChanged(ServerWindow* window) {
 
 void EventDispatcher::OnWindowDestroyed(ServerWindow* window) {
   CancelPointerEventsToTarget(window);
+
+  if (mouse_cursor_source_window_ == window)
+    mouse_cursor_source_window_ = nullptr;
 }
 
 }  // namespace ws