Fix tab drag and drop with hi-dpi.

ui/views/widget/desktop_aura/x11_topmost_window_finder.cc

Index: ui/views/widget/desktop_aura/x11_topmost_window_finder.cc
diff --git a/ui/views/widget/desktop_aura/x11_topmost_window_finder.cc b/ui/views/widget/desktop_aura/x11_topmost_window_finder.cc
index d59b46cf3798755f1bfc8a11995b0723e64cbc18..cdb6aca33cf0725f4b5fb0ba16b06c0815e62fe1 100644
--- a/ui/views/widget/desktop_aura/x11_topmost_window_finder.cc
+++ b/ui/views/widget/desktop_aura/x11_topmost_window_finder.cc
@@ -8,10 +8,24 @@
 
 #include "ui/aura/client/screen_position_client.h"
 #include "ui/aura/window.h"
+#include "ui/gfx/screen.h"
 #include "ui/views/widget/desktop_aura/desktop_window_tree_host_x11.h"
 
 namespace views {
 
+float GetDeviceScaleFactor() {
+  gfx::Display display = gfx::Screen::GetNativeScreen()->GetPrimaryDisplay();
+  return display.device_scale_factor();
+}
+
+gfx::Point ScreenToDIPPoint(const gfx::Point& pixel_point) {
+  return ToFlooredPoint(ScalePoint(pixel_point, 1.0f / GetDeviceScaleFactor()));
+}
+
+gfx::Point DIPToScreenPoint(const gfx::Point& dip_point) {
+  return ToFlooredPoint(gfx::ScalePoint(dip_point, GetDeviceScaleFactor()));
+}
+
 X11TopmostWindowFinder::X11TopmostWindowFinder() : toplevel_(None) {
 }
 
@@ -21,7 +35,7 @@ X11TopmostWindowFinder::~X11TopmostWindowFinder() {
 aura::Window* X11TopmostWindowFinder::FindLocalProcessWindowAt(
     const gfx::Point& screen_loc,
     const std::set<aura::Window*>& ignore) {
-  screen_loc_ = screen_loc;
+  screen_loc_ = DIPToScreenPoint(screen_loc);
   ignore_ = ignore;
 
   std::vector<aura::Window*> local_process_windows =
@@ -41,7 +55,7 @@ aura::Window* X11TopmostWindowFinder::FindLocalProcessWindowAt(
 }
 
 XID X11TopmostWindowFinder::FindWindowAt(const gfx::Point& screen_loc) {
-  screen_loc_ = screen_loc;
+  screen_loc_ = DIPToScreenPoint(screen_loc);

[sadrul, 2015/03/17 15:56:06]

From some of the callsites, the |screen_loc| looks like it should already be in
pixels?

[stapelberg, 2015/03/19 08:25:44]

You’re right. Reverted that part of the change.

   ui::EnumerateTopLevelWindows(this);
   return toplevel_;
 }