exo: Fix dragging edge cases

components/exo/display.h

Index: components/exo/display.h
diff --git a/components/exo/display.h b/components/exo/display.h
index d4f3b3d08065b522f902612fe7fabe6c23a806de..f841c94e74c21568f6c0ff5f04ad428e6ef09307 100644
--- a/components/exo/display.h
+++ b/components/exo/display.h
@@ -12,6 +12,7 @@
 
 #include "base/macros.h"
 #include "base/memory/shared_memory_handle.h"
+#include "ui/gfx/geometry/point.h"
 
 #if defined(USE_OZONE)
 #include "base/files/scoped_file.h"
@@ -20,10 +21,6 @@
 #include "ui/gfx/native_pixmap_handle.h"
 #endif
 
-namespace gfx {
-class Point;
-}
-
 namespace exo {
 class NotificationSurface;
 class NotificationSurfaceManager;
@@ -45,6 +42,20 @@ class Display {
   explicit Display(NotificationSurfaceManager* notification_surface_manager);
   ~Display();
 
+  void set_virtual_origin(const gfx::Point& virtual_origin) {
+    virtual_origin_ = virtual_origin;
+  }
+
+  template <typename Point>
+  void ConvertFromVirtualToScreen(Point* point) const {
+    *point += virtual_origin_.OffsetFromOrigin();
+  }
+
+  template <typename Point>
+  void ConvertFromScreenToVirtual(Point* point) const {
+    *point -= virtual_origin_.OffsetFromOrigin();
+  }
+
   // Creates a new surface.
   std::unique_ptr<Surface> CreateSurface();
 
@@ -88,6 +99,9 @@ class Display {
       const std::string& notification_id);
 
  private:
+  // Origin of the virtual screen relative to the primary display.
+  gfx::Point virtual_origin_;
+
   NotificationSurfaceManager* const notification_surface_manager_;
 
   DISALLOW_COPY_AND_ASSIGN(Display);