Add shortcut keys to ui scaling

ui/aura/root_window.cc

Index: ui/aura/root_window.cc
diff --git a/ui/aura/root_window.cc b/ui/aura/root_window.cc
index c2a63a58f329d3728c691ea74ac427aa3f4d9ba4..d5c041f2007bdc8a9c705671fc41c0f879bd9144 100644
--- a/ui/aura/root_window.cc
+++ b/ui/aura/root_window.cc
@@ -36,8 +36,8 @@
 #include "ui/gfx/display.h"
 #include "ui/gfx/point3_f.h"
 #include "ui/gfx/point_conversions.h"
-#include "ui/gfx/rect_conversions.h"
 #include "ui/gfx/screen.h"
+#include "ui/gfx/size_conversions.h"
 
 using std::vector;
 
@@ -759,7 +759,6 @@ void RootWindow::UpdateWindowSize(const gfx::Size& host_size) {
   bounds = ui::ConvertRectToDIP(layer(), bounds);
   gfx::RectF new_bounds(bounds);
   layer()->transform().TransformRect(&new_bounds);
-
   // It makes little sense to scale beyond the original
   // resolution.
   DCHECK_LE(root_window_scale_, GetDeviceScaleFactor());
@@ -770,7 +769,10 @@ void RootWindow::UpdateWindowSize(const gfx::Size& host_size) {
   new_bounds.Scale(root_window_scale_ * root_window_scale_);
   // Ignore the origin because RootWindow's insets are handled by
   // the transform.
-  SetBounds(gfx::Rect(gfx::ToNearestRect(new_bounds).size()));
+  // Round the size because the bounds is no longer aligned to
+  // backing pixel when |root_window_scale_| is specified
+  // (850 height at 1.25 scale becomes 1062.5 for example.)
+  SetBounds(gfx::Rect(gfx::ToRoundedSize(new_bounds.size())));
 }
 
 void RootWindow::OnWindowAddedToRootWindow(Window* attached) {