Cache scrollbar thickness in LayoutThemeDefault.

third_party/WebKit/Source/core/layout/LayoutThemeDefault.cpp

 /*
  * Copyright (C) 2007 Apple Inc.
  * Copyright (C) 2007 Alp Toker <alp@atoker.com>
  * Copyright (C) 2008 Collabora Ltd.
  * Copyright (C) 2008, 2009 Google Inc.
  * Copyright (C) 2009 Kenneth Rohde Christiansen
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
@@ skipping 317 matching lines @@
 int LayoutThemeDefault::popupInternalPaddingTop(
     const ComputedStyle& style) const {
   return menuListInternalPadding(style, 1);
 }
 
 int LayoutThemeDefault::popupInternalPaddingBottom(
     const ComputedStyle& style) const {
   return menuListInternalPadding(style, 1);
 }
 
-// static
-int LayoutThemeDefault::scrollbarThicknessInDIP() {
+int LayoutThemeDefault::scrollbarThicknessInDIP() const {
+  if (m_scrollbarThicknessInDIP > 0)

[keishi, 2016/12/14 08:23:08]

nit: Maybe initial value should be a negative value in case zero width overlay
scrollbar becomes the default?
https://plus.google.com/+FrancoisBeaufort/posts/XTjX1GGVpjZ?sfc=true

[tkent, 2016/12/14 08:49:40]

AFAIK, getSize(WebThemeEngine::PartScrollbarUpArrow) won't be changed by overlay
scrollbar.  blink::ScrollbarTheme is sensitive to overlay scrollbar, but
WebThemeEngine is in a lower layer than ScrollbatTheme.

I'll add more comments by a follow-up CL.

+    return m_scrollbarThicknessInDIP;
   int width = Platform::current()
                   ->themeEngine()
                   ->getSize(WebThemeEngine::PartScrollbarUpArrow)
                   .width;
-  return width > 0 ? width : 15;
+  const_cast<LayoutThemeDefault*>(this)->m_scrollbarThicknessInDIP =
+      width > 0 ? width : 15;
+  return m_scrollbarThicknessInDIP;
 }
 
-// static
 float LayoutThemeDefault::clampedMenuListArrowPaddingSize(
     const HostWindow* host,
-    const ComputedStyle& style) {
+    const ComputedStyle& style) const {
   int originalSize = scrollbarThicknessInDIP();
   int scaledSize =
       host ? host->windowToViewportScalar(originalSize) : originalSize;
   // The result should not be samller than the scrollbar thickness in order to
   // secure space for scrollbar in popup.
   float deviceScale = 1.0f * scaledSize / originalSize;
   if (style.effectiveZoom() < deviceScale)
     return scaledSize;
   // The value should be zoomed though scrollbars aren't scaled by zoom.
   // crbug.com/432795.
@@ skipping 21 matching lines @@
 double LayoutThemeDefault::animationRepeatIntervalForProgressBar() const {
   return progressAnimationInterval;
 }
 
 double LayoutThemeDefault::animationDurationForProgressBar() const {
   return progressAnimationInterval * progressAnimationFrames *
          2;  // "2" for back and forth
 }
 
 }  // namespace blink