Aura-Mus: Fix high-DPI gutter

ui/aura/mus/client_surface_embedder.cc

Index: ui/aura/mus/client_surface_embedder.cc
diff --git a/ui/aura/mus/client_surface_embedder.cc b/ui/aura/mus/client_surface_embedder.cc
index 94ad333da35c65548becc266d33d6c1deaeb255f..4458206266e05b3322dc1170b2e4aed70fbab637 100644
--- a/ui/aura/mus/client_surface_embedder.cc
+++ b/ui/aura/mus/client_surface_embedder.cc
@@ -6,6 +6,7 @@
 
 #include "cc/surfaces/surface_reference_factory.h"
 #include "ui/aura/window.h"
+#include "ui/gfx/geometry/dip_util.h"
 
 namespace aura {
 namespace {
@@ -65,22 +66,26 @@ void ClientSurfaceEmbedder::SetFallbackSurfaceInfo(
 
 void ClientSurfaceEmbedder::UpdateSizeAndGutters() {
   surface_layer_->SetBounds(gfx::Rect(window_->bounds().size()));
-  // TODO(fsamuel): Fix this for high DPI.
-  gfx::Size fallback_surface_size(
-      surface_layer_->GetFallbackSurfaceInfo()
-          ? surface_layer_->GetFallbackSurfaceInfo()->size_in_pixels()
-          : gfx::Size());
+  gfx::Size fallback_surface_size_in_dip;
+  const cc::SurfaceInfo* fallback_surface_info =
+      surface_layer_->GetFallbackSurfaceInfo();
+  if (fallback_surface_info) {
+    float fallback_device_scale_factor =
+        fallback_surface_info->device_scale_factor();
+    fallback_surface_size_in_dip = gfx::ConvertSizeToDIP(
+        fallback_device_scale_factor, fallback_surface_info->size_in_pixels());
+  }
   gfx::Rect window_bounds(window_->bounds());
-  if (fallback_surface_size.width() < window_bounds.width()) {
+  if (fallback_surface_size_in_dip.width() < window_bounds.width()) {
     right_gutter_ = base::MakeUnique<ui::Layer>(ui::LAYER_SOLID_COLOR);
     // TODO(fsamuel): Use the embedded client's background color.
     right_gutter_->SetColor(SK_ColorWHITE);
-    int width = window_bounds.width() - fallback_surface_size.width();
+    int width = window_bounds.width() - fallback_surface_size_in_dip.width();
     // The right gutter also includes the bottom-right corner, if necessary.
     int height = window_bounds.height() - client_area_insets_.height();
-    right_gutter_->SetBounds(
-        gfx::Rect(client_area_insets_.left() + fallback_surface_size.width(),
-                  client_area_insets_.top(), width, height));
+    right_gutter_->SetBounds(gfx::Rect(
+        client_area_insets_.left() + fallback_surface_size_in_dip.width(),
+        client_area_insets_.top(), width, height));
     window_->layer()->Add(right_gutter_.get());
   } else {
     right_gutter_.reset();
@@ -88,15 +93,15 @@ void ClientSurfaceEmbedder::UpdateSizeAndGutters() {
 
   // Only create a bottom gutter if a fallback surface is available. Otherwise,
   // the right gutter will fill the whole window until a fallback is available.
-  if (!fallback_surface_size.IsEmpty() &&
-      fallback_surface_size.height() < window_bounds.height()) {
+  if (!fallback_surface_size_in_dip.IsEmpty() &&
+      fallback_surface_size_in_dip.height() < window_bounds.height()) {
     bottom_gutter_ = base::MakeUnique<ui::Layer>(ui::LAYER_SOLID_COLOR);
     // TODO(fsamuel): Use the embedded client's background color.
     bottom_gutter_->SetColor(SK_ColorWHITE);
-    int width = fallback_surface_size.width();
-    int height = window_bounds.height() - fallback_surface_size.height();
+    int width = fallback_surface_size_in_dip.width();
+    int height = window_bounds.height() - fallback_surface_size_in_dip.height();
     bottom_gutter_->SetBounds(
-        gfx::Rect(0, fallback_surface_size.height(), width, height));
+        gfx::Rect(0, fallback_surface_size_in_dip.height(), width, height));
     window_->layer()->Add(bottom_gutter_.get());
   } else {
     bottom_gutter_.reset();