Make DesktopScreenX11::GetWindowAtScreenPoint() take non-Chrome windows into account

ui/views/widget/desktop_aura/desktop_screen_x11.cc

Index: ui/views/widget/desktop_aura/desktop_screen_x11.cc
diff --git a/ui/views/widget/desktop_aura/desktop_screen_x11.cc b/ui/views/widget/desktop_aura/desktop_screen_x11.cc
index 271e4ec558a10b10a81d0ad439906dfc37254100..9753fde44c81d050ef23fa9121cbd9c40731bbcf 100644
--- a/ui/views/widget/desktop_aura/desktop_screen_x11.cc
+++ b/ui/views/widget/desktop_aura/desktop_screen_x11.cc
@@ -63,6 +63,50 @@ std::vector<gfx::Display> GetFallbackDisplayList() {
   return std::vector<gfx::Display>(1, gfx_display);
 }
 
+// Helper class to GetWindowAtScreenPoint() which returns the topmost window at
+// the location passed to FindAt(). NULL is returned if a window which does not
+// belong to Chromium is topmost at the passed in location.
+class ToplevelWindowFinder : public ui::EnumerateWindowsDelegate {
+ public:
+  ToplevelWindowFinder() : toplevel_(NULL) {
+  }
+
+  virtual ~ToplevelWindowFinder() {
+  }
+
+  aura::Window* FindAt(const gfx::Point& screen_loc) {
+    screen_loc_ = screen_loc;
+    ui::EnumerateTopLevelWindows(this);
+    return toplevel_;
+  }
+
+ protected:
+  virtual bool ShouldStopIterating(XID xid) OVERRIDE {
+    aura::Window* window =
+        views::DesktopWindowTreeHostX11::GetContentWindowForXID(xid);
+    if (window) {
+      if (window->IsVisible() &&
+          window->GetBoundsInScreen().Contains(screen_loc_)) {
+        toplevel_ = window;
+        return true;
+      }
+      return false;
+    }
+
+    if (ui::IsWindowVisible(xid) &&
+        ui::WindowContainsPoint(xid, screen_loc_)) {
+      // toplevel_ = NULL
+      return true;
+    }
+    return false;
+  }
+
+  gfx::Point screen_loc_;
+  aura::Window* toplevel_;
+
+  DISALLOW_COPY_AND_ASSIGN(ToplevelWindowFinder);
+};
+
 }  // namespace
 
 namespace views {
@@ -182,16 +226,8 @@ gfx::NativeWindow DesktopScreenX11::GetWindowUnderCursor() {
 
 gfx::NativeWindow DesktopScreenX11::GetWindowAtScreenPoint(
     const gfx::Point& point) {
-  std::vector<aura::Window*> windows =
-      DesktopWindowTreeHostX11::GetAllOpenWindows();
-
-  for (std::vector<aura::Window*>::const_iterator it = windows.begin();
-       it != windows.end(); ++it) {
-    if ((*it)->GetBoundsInScreen().Contains(point))
-      return *it;
-  }
-
-  return NULL;
+  ToplevelWindowFinder finder;
+  return finder.FindAt(point);
 }
 
 int DesktopScreenX11::GetNumDisplays() const {