Revert of Calculate paint invalidation rect for scrollbars

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

Index: third_party/WebKit/Source/platform/scroll/ScrollbarTheme.cpp
diff --git a/third_party/WebKit/Source/platform/scroll/ScrollbarTheme.cpp b/third_party/WebKit/Source/platform/scroll/ScrollbarTheme.cpp
index 601dc30aa70d2280b0bbfe66cb227aa844199924..9a1b08e5f1e06dd64991235e9f8b697a7a429875 100644
--- a/third_party/WebKit/Source/platform/scroll/ScrollbarTheme.cpp
+++ b/third_party/WebKit/Source/platform/scroll/ScrollbarTheme.cpp
@@ -170,6 +170,46 @@
     return result;
 }
 
+void ScrollbarTheme::invalidatePart(ScrollbarThemeClient* scrollbar, ScrollbarPart part)
+{
+    if (part == NoPart)
+        return;
+
+    IntRect result;
+    switch (part) {
+    case BackButtonStartPart:
+        result = backButtonRect(scrollbar, BackButtonStartPart, true);
+        break;
+    case BackButtonEndPart:
+        result = backButtonRect(scrollbar, BackButtonEndPart, true);
+        break;
+    case ForwardButtonStartPart:
+        result = forwardButtonRect(scrollbar, ForwardButtonStartPart, true);
+        break;
+    case ForwardButtonEndPart:
+        result = forwardButtonRect(scrollbar, ForwardButtonEndPart, true);
+        break;
+    case TrackBGPart:
+        result = trackRect(scrollbar, true);
+        break;
+    case ScrollbarBGPart:
+        result = scrollbar->frameRect();
+        break;
+    default: {
+        IntRect beforeThumbRect, thumbRect, afterThumbRect;
+        splitTrack(scrollbar, trackRect(scrollbar), beforeThumbRect, thumbRect, afterThumbRect);
+        if (part == BackTrackPart)
+            result = beforeThumbRect;
+        else if (part == ForwardTrackPart)
+            result = afterThumbRect;
+        else
+            result = thumbRect;
+    }
+    }
+    result.moveBy(-scrollbar->location());
+    scrollbar->invalidateRect(result);
+}
+
 void ScrollbarTheme::paintScrollCorner(GraphicsContext* context, const DisplayItemClientWrapper& displayItemClient, const IntRect& cornerRect)
 {
     if (cornerRect.isEmpty())