Mac: Don't repaint scrollbars every frame

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

Index: third_party/WebKit/Source/platform/scroll/ScrollbarThemeMock.cpp
diff --git a/third_party/WebKit/Source/platform/scroll/ScrollbarThemeMock.cpp b/third_party/WebKit/Source/platform/scroll/ScrollbarThemeMock.cpp
index 61d91d468921f0cc99e1d238f8fde26182891e51..4007cbb6655e4ff942f4ac47e0c4a8f342b44e58 100644
--- a/third_party/WebKit/Source/platform/scroll/ScrollbarThemeMock.cpp
+++ b/third_party/WebKit/Source/platform/scroll/ScrollbarThemeMock.cpp
@@ -33,13 +33,15 @@
 
 namespace blink {
 
-static int cScrollbarThickness[] = { 15, 11 };
+static bool gShouldRepaintAllPartsOnInvalidation = true;
 
-IntRect ScrollbarThemeMock::trackRect(const ScrollbarThemeClient* scrollbar, bool)
+void ScrollbarThemeMock::setShouldRepaintAllPartsOnInvalidation(bool shouldRepaint)
 {
-    return scrollbar->frameRect();
+    gShouldRepaintAllPartsOnInvalidation = shouldRepaint;
 }
 
+static int cScrollbarThickness[] = { 15, 11 };
+
 int ScrollbarThemeMock::scrollbarThickness(ScrollbarControlSize controlSize)
 {
     return cScrollbarThickness[controlSize];
@@ -50,6 +52,17 @@ bool ScrollbarThemeMock::usesOverlayScrollbars() const
     return RuntimeEnabledFeatures::overlayScrollbarsEnabled();
 }
 
+bool ScrollbarThemeMock::shouldRepaintAllPartsOnInvalidation() const
+{
+    return gShouldRepaintAllPartsOnInvalidation;
+}
+
+IntRect ScrollbarThemeMock::trackRect(const ScrollbarThemeClient* scrollbar, bool)
+{
+    return scrollbar->frameRect();
+}
+
+
 void ScrollbarThemeMock::paintTrackBackground(GraphicsContext* context, const ScrollbarThemeClient* scrollbar, const IntRect& trackRect)
 {
     if (DrawingRecorder::useCachedDrawingIfPossible(*context, *scrollbar, DisplayItem::ScrollbarTrackBackground))