Allow the cursor to warp even when a window is dragged

ash/display/mouse_cursor_event_filter.cc

Index: ash/display/mouse_cursor_event_filter.cc
diff --git a/ash/display/mouse_cursor_event_filter.cc b/ash/display/mouse_cursor_event_filter.cc
index 9b6d2973cde40375253e5cd909298ce5305d84bc..f958ce791a1649ba465b7d612940175bf289db05 100644
--- a/ash/display/mouse_cursor_event_filter.cc
+++ b/ash/display/mouse_cursor_event_filter.cc
@@ -7,6 +7,7 @@
 #include "ash/display/display_controller.h"
 #include "ash/shell.h"
 #include "ash/wm/cursor_manager.h"
+#include "ui/aura/client/screen_position_client.h"
 #include "ui/aura/env.h"
 #include "ui/aura/event.h"
 #include "ui/aura/root_window.h"
@@ -31,14 +32,33 @@ bool MouseCursorEventFilter::PreHandleKeyEvent(aura::Window* target,
 
 bool MouseCursorEventFilter::PreHandleMouseEvent(aura::Window* target,
                                                  aura::MouseEvent* event) {
-  if (event->type() != ui::ET_MOUSE_MOVED ||
-      ash::Shell::GetInstance()->cursor_manager()->is_cursor_locked())
-    return false;
-  aura::RootWindow* current_root = target->GetRootWindow();
+  const bool is_cursor_locked =
+      Shell::GetInstance()->cursor_manager()->is_cursor_locked();
+
+  // When the cursor is not locked (i.e., nothing is dragged), we only handle
+  // ET_MOUSE_MOVED events. When it's locked, we only handle ET_MOUSE_DRAGGED
+  // events. This is because when the cursor enters the other root window while
+  // dragging, the underlying window system (at least X11) stops generating an
+  // ET_MOUSE_MOVED event.
+  if (!is_cursor_locked) {
+    if (event->type() != ui::ET_MOUSE_MOVED)
+      return false;
+  } else {
+    if (event->type() != ui::ET_MOUSE_DRAGGED)
+      return false;
+  }
+
   gfx::Point location_in_root(event->location());
-  aura::Window::ConvertPointToWindow(target, current_root, &location_in_root);
+  aura::Window::ConvertPointToWindow(
+      target, target->GetRootWindow(), &location_in_root);
+
+  // Get the root window where the cursor is currently on, then pass the window
+  // and the location in the window's coordinates to ash::DisplayController.
+  std::pair<aura::RootWindow*, gfx::Point> actual_location =
+      Shell::GetInstance()->NormalizeLocationInDragEvent(
+          target->GetRootWindow(), location_in_root);
   return display_controller_->WarpMouseCursorIfNecessary(
-      current_root, location_in_root);
+      actual_location.first, actual_location.second, is_cursor_locked);
 }
 
 ui::TouchStatus MouseCursorEventFilter::PreHandleTouchEvent(