Use nine-patch resource for drawing Aura overlay scrollbar thumb.

third_party/WebKit/Source/platform/scroll/ScrollbarThemeOverlay.cpp

Index: third_party/WebKit/Source/platform/scroll/ScrollbarThemeOverlay.cpp
diff --git a/third_party/WebKit/Source/platform/scroll/ScrollbarThemeOverlay.cpp b/third_party/WebKit/Source/platform/scroll/ScrollbarThemeOverlay.cpp
index 9753dcc192827a0a56e415c39e9afe1f31795f66..532136f23bb54c35d575b8049de028b1d8ae93b1 100644
--- a/third_party/WebKit/Source/platform/scroll/ScrollbarThemeOverlay.cpp
+++ b/third_party/WebKit/Source/platform/scroll/ScrollbarThemeOverlay.cpp
@@ -236,4 +236,37 @@ ScrollbarThemeOverlay& ScrollbarThemeOverlay::mobileTheme() {
   return *theme;
 }
 
+bool ScrollbarThemeOverlay::usesNinePatchThumbResource() const {
+  WebThemeEngine* engine = Platform::current()->themeEngine();
+  if (!engine)
+    return false;
+
+  // Thumb orientation doesn't matter here.
+  return engine->supportsNinePatch(WebThemeEngine::PartScrollbarVerticalThumb);
+}
+
+IntSize ScrollbarThemeOverlay::ninePatchThumbCanvasSize(
+    const ScrollbarThemeClient& scrollbar) const {
+  DCHECK(usesNinePatchThumbResource());
+
+  WebThemeEngine::Part part = WebThemeEngine::PartScrollbarHorizontalThumb;

[jbroman, 2017/03/01 15:27:18]

super-nit: for something this simple why not a ternary?

WebThemeEngine::Part part = scrollbar.orientation() == VerticalScrollbar
    ? WebThemeEngine::PartScrollbarVerticalThumb
    : WebThemeEngine::PartScrollbarHorizontalThumb;

Seems a little clearer to me than assigning and then reassigning the variable,
but up to you.

[bokan, 2017/03/01 16:22:45]

Done.

+  if (scrollbar.orientation() == VerticalScrollbar)
+    part = WebThemeEngine::PartScrollbarVerticalThumb;
+
+  DCHECK(Platform::current()->themeEngine());
+  return Platform::current()->themeEngine()->ninePatchCanvasSize(part);
+}
+
+IntRect ScrollbarThemeOverlay::ninePatchThumbAperture(
+    const ScrollbarThemeClient& scrollbar) const {
+  DCHECK(usesNinePatchThumbResource());
+
+  WebThemeEngine::Part part = WebThemeEngine::PartScrollbarHorizontalThumb;
+  if (scrollbar.orientation() == VerticalScrollbar)
+    part = WebThemeEngine::PartScrollbarVerticalThumb;
+
+  DCHECK(Platform::current()->themeEngine());
+  return Platform::current()->themeEngine()->ninePatchAperture(part);
+}
+
 }  // namespace blink