Cache scrollbar thickness in LayoutThemeDefault.

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

Index: third_party/WebKit/Source/core/layout/LayoutThemeDefault.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutThemeDefault.cpp b/third_party/WebKit/Source/core/layout/LayoutThemeDefault.cpp
index e0d778f384951b8d32008ea19ac60b2d97978c20..39e0c091e08542627ef03e4bab07aeab36fa7192 100644
--- a/third_party/WebKit/Source/core/layout/LayoutThemeDefault.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutThemeDefault.cpp
@@ -335,19 +335,21 @@ int LayoutThemeDefault::popupInternalPaddingBottom(
   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;