Resizes corner rect to match device scale factor

third_party/WebKit/Source/core/paint/ScrollableAreaPainter.cpp

Index: third_party/WebKit/Source/core/paint/ScrollableAreaPainter.cpp
diff --git a/third_party/WebKit/Source/core/paint/ScrollableAreaPainter.cpp b/third_party/WebKit/Source/core/paint/ScrollableAreaPainter.cpp
index 94dea2f946012bb7ed79767469cd526dadcfb809..f2d7302e64a1f19f3939a487836f16b63f72ba81 100644
--- a/third_party/WebKit/Source/core/paint/ScrollableAreaPainter.cpp
+++ b/third_party/WebKit/Source/core/paint/ScrollableAreaPainter.cpp
@@ -13,6 +13,7 @@
 #include "core/paint/PaintLayerScrollableArea.h"
 #include "core/paint/ScrollbarPainter.h"
 #include "core/paint/TransformRecorder.h"
+#include "platform/HostWindow.h"
 #include "platform/graphics/GraphicsContext.h"
 #include "platform/graphics/GraphicsContextStateSaver.h"
 #include "platform/graphics/paint/ClipRecorder.h"
@@ -68,8 +69,13 @@ void ScrollableAreaPainter::paintResizer(GraphicsContext& context,
 void ScrollableAreaPainter::drawPlatformResizerImage(
     GraphicsContext& context,
     IntRect resizerCornerRect) {
+  // |blink::deviceScaleFactor| returns different values between MAC (2 or 1)
+  // and other platforms (always 1). For this reason we cannot hardcode the
+  // value of 1 in the call for |windowToViewportScalar|. Since zoom-for-dsf is
+  // disabled on MAC, |windowToViewportScalar| will be a no-op on it.
   float deviceScaleFactor =
-      blink::deviceScaleFactor(getScrollableArea().box().frame());
+      getScrollableArea().getHostWindow()->windowToViewportScalar(
+          blink::deviceScaleFactor(getScrollableArea().box().frame()));
 
   RefPtr<Image> resizeCornerImage;
   IntSize cornerResizerSize;
@@ -78,7 +84,8 @@ void ScrollableAreaPainter::drawPlatformResizerImage(
                       (Image::loadPlatformResource("textAreaResizeCorner@2x")));
     resizeCornerImage = resizeCornerImageHiRes;
     cornerResizerSize = resizeCornerImage->size();
-    cornerResizerSize.scale(0.5f);
+    if (blink::deviceScaleFactor(getScrollableArea().box().frame()) >= 2)

[oshima, 2017/02/17 16:59:59]

nit: cache this value first, like

float oldBlinkDeviceScaleFactor = .

then use it both above and here.

+      cornerResizerSize.scale(0.5f);
   } else {
     DEFINE_STATIC_REF(Image, resizeCornerImageLoRes,
                       (Image::loadPlatformResource("textAreaResizeCorner")));