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

third_party/WebKit/Source/platform/exported/WebScrollbarThemeGeometryNative.cpp

Index: third_party/WebKit/Source/platform/exported/WebScrollbarThemeGeometryNative.cpp
diff --git a/third_party/WebKit/Source/platform/exported/WebScrollbarThemeGeometryNative.cpp b/third_party/WebKit/Source/platform/exported/WebScrollbarThemeGeometryNative.cpp
index 157dacadef7af127226d358956f2a3dd79b1ae82..be7bd6954994ce94002e98e98fedf20d1e383b24 100644
--- a/third_party/WebKit/Source/platform/exported/WebScrollbarThemeGeometryNative.cpp
+++ b/third_party/WebKit/Source/platform/exported/WebScrollbarThemeGeometryNative.cpp
@@ -82,4 +82,18 @@ WebRect WebScrollbarThemeGeometryNative::forwardButtonEndRect(
                                    ForwardButtonEndPart, false);
 }
 
+WebSize WebScrollbarThemeGeometryNative::ninePatchThumbCanvasSize(
+    WebScrollbar* scrollbar) {
+  DCHECK(m_theme.usesNinePatchThumbResource());
+  return m_theme.ninePatchThumbCanvasSize(
+      WebScrollbarThemeClientImpl(*scrollbar));
+}
+
+WebRect WebScrollbarThemeGeometryNative::ninePatchThumbAperture(
+    WebScrollbar* scrollbar) {
+  DCHECK(m_theme.usesNinePatchThumbResource());
+  return m_theme.ninePatchThumbAperture(
+      WebScrollbarThemeClientImpl(*scrollbar));
+}
+
 }  // namespace blink