From d1f5731c04c6e90de70f5947655e61ae632c30b9 Mon Sep 17 00:00:00 2001
From: Emilio Cobos Alvarez <emilio@crisal.io>
Date: Mon, 30 Aug 2021 18:01:44 +0000
Subject: [PATCH] Bug 1727289 - Prefer widget scale for scrollbar parts.
 r=mstange

Print preview documents might use a different DPI depending on the print
target.

Differential Revision: https://phabricator.services.mozilla.com/D123939
---
 widget/nsNativeBasicTheme.cpp | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/widget/nsNativeBasicTheme.cpp b/widget/nsNativeBasicTheme.cpp
index 989ac5fdfdd1..1484f4f432c8 100644
--- a/widget/nsNativeBasicTheme.cpp
+++ b/widget/nsNativeBasicTheme.cpp
@@ -342,6 +342,9 @@ static std::pair<sRGBColor, sRGBColor> SystemColorPair(
 /* static */
 auto nsNativeBasicTheme::GetDPIRatioForScrollbarPart(nsPresContext* aPc)
     -> DPIRatio {
+  if (auto* widget = aPc->GetRootPresContext()->GetRootWidget()) {
+    return widget->GetDefaultScale();
+  }
   return DPIRatio(float(AppUnitsPerCSSPixel()) /
                   aPc->DeviceContext()->AppUnitsPerDevPixelAtUnitFullZoom());
 }