Fix high-DPI on Windows to make use of DIP scaling in WebKit.

ui/surface/accelerated_surface_win.cc

Index: ui/surface/accelerated_surface_win.cc
diff --git a/ui/surface/accelerated_surface_win.cc b/ui/surface/accelerated_surface_win.cc
index 8e6e8094b84737f750296fb209e38c54fb8c4c6f..2b71aa598e1ca406b28f25683f5d0dd4012caf10 100644
--- a/ui/surface/accelerated_surface_win.cc
+++ b/ui/surface/accelerated_surface_win.cc
@@ -23,6 +23,7 @@
 #include "base/threading/thread_restrictions.h"
 #include "base/time.h"
 #include "base/win/wrapped_window_proc.h"
+#include "ui/base/win/dpi.h"
 #include "ui/base/win/hwnd_util.h"
 #include "ui/gfx/rect.h"
 #include "ui/gl/gl_switches.h"
@@ -489,7 +490,19 @@ void AcceleratedPresenter::DoPresentAndAcknowledge(
   // If the window is a different size than the swap chain that is being
   // presented then drop the frame.
   gfx::Size window_size = GetWindowSize();
-  if (hidden_ && size != window_size) {
+#if defined(ENABLE_HIDPI)
+  // Check if the size mismatch is within allowable round off or truncation
+  // error.
+  gfx::Size dip_size = ui::win::ScreenToDIPSize(window_size);
+  gfx::Size pixel_size = ui::win::DIPToScreenSize(dip_size);
+  bool size_mismatch = abs(window_size.width() - size.width()) >
+      abs(window_size.width() - pixel_size.width()) ||
+      abs(window_size.height() - size.height()) >
+      abs(window_size.height() - pixel_size.height());
+#else
+  bool size_mismatch = size != window_size;
+#endif
+  if (hidden_ && size_mismatch) {
     TRACE_EVENT2("gpu", "EarlyOut_WrongWindowSize",
                  "backwidth", size.width(), "backheight", size.height());
     TRACE_EVENT2("gpu", "EarlyOut_WrongWindowSize2",