Resizes corner rect to match device scale factor

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

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/paint/ScrollableAreaPainter.h"
 
 #include "core/layout/LayoutView.h"
 #include "core/page/Page.h"
 #include "core/paint/LayoutObjectDrawingRecorder.h"
 #include "core/paint/ObjectPaintProperties.h"
 #include "core/paint/PaintInfo.h"
 #include "core/paint/PaintLayer.h"
 #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"
 #include "platform/graphics/paint/ScopedPaintChunkProperties.h"
 
 namespace blink {
 
 void ScrollableAreaPainter::paintResizer(GraphicsContext& context,
                                          const IntPoint& paintOffset,
                                          const CullRect& cullRect) {
@@ skipping 35 matching lines @@
     context.setStrokeColor(Color(217, 217, 217));
     context.setStrokeThickness(1.0f);
     context.setFillColor(Color::transparent);
     context.drawRect(largerCorner);
   }
 }
 
 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;
   if (deviceScaleFactor >= 2) {
     DEFINE_STATIC_REF(Image, resizeCornerImageHiRes,
                       (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")));
     resizeCornerImage = resizeCornerImageLoRes;
     cornerResizerSize = resizeCornerImage->size();
   }
 
   if (getScrollableArea()
           .box()
           .shouldPlaceBlockDirectionScrollbarOnLogicalLeft()) {
@@ skipping 163 matching lines @@
   LayoutObjectDrawingRecorder recorder(context, getScrollableArea().box(),
                                        DisplayItem::kScrollbarCorner, absRect);
   context.fillRect(absRect, Color::white);
 }
 
 PaintLayerScrollableArea& ScrollableAreaPainter::getScrollableArea() const {
   return *m_scrollableArea;
 }
 
 }  // namespace blink