mus: Allow embedder to intercept events.

components/mus/ws/window_manager_state.cc

Index: components/mus/ws/window_manager_state.cc
diff --git a/components/mus/ws/window_manager_state.cc b/components/mus/ws/window_manager_state.cc
index b28716005977f1d07a0ca2b0723b2daec27c7a9c..51a08e253baecd7872f0181f77c0fe1fefaa31ee 100644
--- a/components/mus/ws/window_manager_state.cc
+++ b/components/mus/ws/window_manager_state.cc
@@ -55,6 +55,14 @@ std::unique_ptr<ui::Event> CoalesceEvents(std::unique_ptr<ui::Event> first,
   return second;
 }
 
+ServerWindow* GetEmbedRoot(ServerWindow* window) {
+  DCHECK(window);
+  ServerWindow* embed_root = window->parent();
+  while (embed_root && embed_root->id().client_id == window->id().client_id)
+    embed_root = embed_root->parent();
+  return embed_root;
+}
+
 }  // namespace
 
 class WindowManagerState::ProcessedEventTarget {
@@ -297,22 +305,29 @@ void WindowManagerState::DispatchInputEventToWindowImpl(
   }
 
   // If the event is in the non-client area the event goes to the owner of
-  // the window. Otherwise if the window is an embed root, forward to the
-  // embedded window.
-  WindowTree* tree =
-      in_nonclient_area
-          ? window_server()->GetTreeWithId(target->id().client_id)
-          : window_server()->GetTreeWithRoot(target);
-  if (!tree) {
-    if (in_nonclient_area) {
-      // Being the root of the tree means we may get events outside the bounds
-      // of the platform window. Because the root has a client id of 0,
-      // no WindowTree is found for it and we have to special case it here.
-      DCHECK_EQ(target, root_.get());
-      tree = tree_;
-    } else {
+  // the window.
+  WindowTree* tree = nullptr;
+  if (in_nonclient_area) {
+    tree = window_server()->GetTreeWithId(target->id().client_id);
+  } else {
+    // If the window is an embed root, forward to the embedded window.
+    tree = window_server()->GetTreeWithRoot(target);
+    if (!tree)
       tree = window_server()->GetTreeWithId(target->id().client_id);
-    }
+  }
+
+  ServerWindow* embed_root =
+      tree->HasRoot(target) ? target : GetEmbedRoot(target);
+  while (tree && tree->embedder_intercepts_events()) {
+    DCHECK(tree->HasRoot(embed_root));
+    tree = window_server()->GetTreeWithId(embed_root->id().client_id);
+    embed_root = GetEmbedRoot(embed_root);
+  }
+
+  if (!tree) {
+    DCHECK(in_nonclient_area);
+    DCHECK_EQ(target, root_.get());
+    tree = tree_;
   }
 
   // TOOD(sad): Adjust this delay, possibly make this dynamic.