Simplify calls for scale factor

content/browser/renderer_host/render_widget_host_view_mac.mm

Index: content/browser/renderer_host/render_widget_host_view_mac.mm
diff --git a/content/browser/renderer_host/render_widget_host_view_mac.mm b/content/browser/renderer_host/render_widget_host_view_mac.mm
index b7b6e741b5555a87b1855b7694a229053d5fa045..88a50beb14059439bac21f6d4c1234502c5a1307 100644
--- a/content/browser/renderer_host/render_widget_host_view_mac.mm
+++ b/content/browser/renderer_host/render_widget_host_view_mac.mm
@@ -75,7 +75,6 @@
 #include "ui/base/cocoa/cocoa_base_utils.h"
 #import "ui/base/cocoa/fullscreen_window_manager.h"
 #import "ui/base/cocoa/underlay_opengl_hosting_window.h"
-#include "ui/base/layout.h"
 #include "ui/compositor/compositor.h"
 #include "ui/compositor/layer.h"
 #include "ui/display/display.h"
@@ -475,7 +474,10 @@ RenderWidgetHostViewMac::RenderWidgetHostViewMac(RenderWidgetHost* widget,
       new BrowserCompositorMac(this, this, render_widget_host_->is_hidden(),
                                [cocoa_view_ window], frame_sink_id));
 
-  display::Screen::GetScreen()->AddObserver(this);
+  display::Screen* screen = display::Screen::GetScreen();
+  device_scale_factor_ =
+      screen->GetDisplayNearestWindow(cocoa_view_).device_scale_factor();
+  screen->AddObserver(this);
 
   if (!is_guest_view_hack_)
     render_widget_host_->SetView(this);
@@ -689,10 +691,6 @@ int RenderWidgetHostViewMac::window_number() const {
   return [window windowNumber];
 }
 
-float RenderWidgetHostViewMac::ViewScaleFactor() const {
-  return ui::GetScaleFactorForNativeView(cocoa_view_);
-}
-
 void RenderWidgetHostViewMac::UpdateDisplayLink() {
   static bool is_vsync_disabled =
       base::CommandLine::ForCurrentProcess()->HasSwitch(
@@ -1523,14 +1521,13 @@ cc::FrameSinkId RenderWidgetHostViewMac::FrameSinkIdAtPoint(
     gfx::Point* transformed_point) {
   // The surface hittest happens in device pixels, so we need to convert the
   // |point| from DIPs to pixels before hittesting.
-  float scale_factor = display::Screen::GetScreen()
-                           ->GetDisplayNearestWindow(cocoa_view_)
-                           .device_scale_factor();
-  gfx::Point point_in_pixels = gfx::ConvertPointToPixel(scale_factor, point);
+  gfx::Point point_in_pixels =
+      gfx::ConvertPointToPixel(device_scale_factor_, point);
   cc::SurfaceId id =
       browser_compositor_->GetDelegatedFrameHost()->SurfaceIdAtPoint(
           delegate, point_in_pixels, transformed_point);
-  *transformed_point = gfx::ConvertPointToDIP(scale_factor, *transformed_point);
+  *transformed_point =
+      gfx::ConvertPointToDIP(device_scale_factor_, *transformed_point);
 
   // It is possible that the renderer has not yet produced a surface, in which
   // case we return our current namespace.
@@ -1580,15 +1577,14 @@ bool RenderWidgetHostViewMac::TransformPointToLocalCoordSpace(
     gfx::Point* transformed_point) {
   // Transformations use physical pixels rather than DIP, so conversion
   // is necessary.
-  float scale_factor = display::Screen::GetScreen()
-                           ->GetDisplayNearestWindow(cocoa_view_)
-                           .device_scale_factor();
-  gfx::Point point_in_pixels = gfx::ConvertPointToPixel(scale_factor, point);
+  gfx::Point point_in_pixels =
+      gfx::ConvertPointToPixel(device_scale_factor_, point);
   if (!browser_compositor_->GetDelegatedFrameHost()
            ->TransformPointToLocalCoordSpace(point_in_pixels, original_surface,
                                              transformed_point))
     return false;
-  *transformed_point = gfx::ConvertPointToDIP(scale_factor, *transformed_point);
+  *transformed_point =
+      gfx::ConvertPointToDIP(device_scale_factor_, *transformed_point);
   return true;
 }
 
@@ -1733,8 +1729,9 @@ void RenderWidgetHostViewMac::OnDisplayMetricsChanged(
   if (changed_metrics & DisplayObserver::DISPLAY_METRIC_DEVICE_SCALE_FACTOR) {
     RenderWidgetHostImpl* host =
         RenderWidgetHostImpl::From(GetRenderWidgetHost());
+    device_scale_factor_ = display.device_scale_factor();

[tapted, 2017/03/13 00:02:33]

This isn't quite the same. OnDisplayMetricsChanged() is only triggered when the
display metrics change (e.g. add/remove display, or change resolution). It's
_not_ triggered when the window simply moves to a different display, which is
far more common.

I don't think we should add |device_scale_factor_| to RenderWidgetHostViewMac --
it is duplicating the function of |current_device_scale_factor_| in
RenderWidgetHostViewBase in any case.

But `ui::GetScaleFactorForNativeView(..)` is an inexpensive method call on Mac
under most situations -- we shouldn't worry about caching it - just call it each
time.

[Jinsuk Kim, 2017/03/13 00:25:01]

Reverted the change. Removed an unused method only.

     if (host && host->delegate())
-      host->delegate()->UpdateDeviceScaleFactor(display.device_scale_factor());
+      host->delegate()->UpdateDeviceScaleFactor(device_scale_factor_);
   }
 
   UpdateScreenInfo(cocoa_view_);