Revert of Calculate paint invalidation rect for scrollbars

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

Index: third_party/WebKit/Source/platform/scroll/ScrollableArea.cpp
diff --git a/third_party/WebKit/Source/platform/scroll/ScrollableArea.cpp b/third_party/WebKit/Source/platform/scroll/ScrollableArea.cpp
index 85016be74b5a15c2f326a65e4254a439ceac12f6..f23801b9243c29badaf4540425180ae39d106b05 100644
--- a/third_party/WebKit/Source/platform/scroll/ScrollableArea.cpp
+++ b/third_party/WebKit/Source/platform/scroll/ScrollableArea.cpp
@@ -51,6 +51,7 @@
 
 struct SameSizeAsScrollableArea {
     virtual ~SameSizeAsScrollableArea();
+    IntRect scrollbarDamage[2];
 #if ENABLE(ASSERT) && ENABLE(OILPAN)
     VerifyEagerFinalization verifyEager;
 #endif
@@ -81,9 +82,6 @@
     : m_inLiveResize(false)
     , m_scrollbarOverlayStyle(ScrollbarOverlayStyleDefault)
     , m_scrollOriginChanged(false)
-    , m_horizontalScrollbarNeedsPaintInvalidation(false)
-    , m_verticalScrollbarNeedsPaintInvalidation(false)
-    , m_scrollCornerNeedsPaintInvalidation(false)
 {
 }
 
@@ -248,13 +246,22 @@
     // Tell the scrollbars to update their thumb postions.
     if (Scrollbar* horizontalScrollbar = this->horizontalScrollbar()) {
         horizontalScrollbar->offsetDidChange();
-        if (horizontalScrollbar->isOverlayScrollbar() && !hasLayerForHorizontalScrollbar())
-            setScrollbarNeedsPaintInvalidation(horizontalScrollbar);
+        if (horizontalScrollbar->isOverlayScrollbar() && !hasLayerForHorizontalScrollbar()) {
+            if (!verticalScrollbar)
+                horizontalScrollbar->invalidate();
+            else {
+                // If there is both a horizontalScrollbar and a verticalScrollbar,
+                // then we must also invalidate the corner between them.
+                IntRect boundsAndCorner = horizontalScrollbar->boundsRect();
+                boundsAndCorner.setWidth(boundsAndCorner.width() + verticalScrollbar->width());
+                horizontalScrollbar->invalidateRect(boundsAndCorner);
+            }
+        }
     }
     if (verticalScrollbar) {
         verticalScrollbar->offsetDidChange();
         if (verticalScrollbar->isOverlayScrollbar() && !hasLayerForVerticalScrollbar())
-            setScrollbarNeedsPaintInvalidation(verticalScrollbar);
+            verticalScrollbar->invalidate();
     }
 
     if (scrollPositionDouble() != oldPosition) {
@@ -395,16 +402,16 @@
 
     if (Scrollbar* scrollbar = horizontalScrollbar()) {
         ScrollbarTheme::theme()->updateScrollbarOverlayStyle(scrollbar);
-        setScrollbarNeedsPaintInvalidation(scrollbar);
+        scrollbar->invalidate();
     }
 
     if (Scrollbar* scrollbar = verticalScrollbar()) {
         ScrollbarTheme::theme()->updateScrollbarOverlayStyle(scrollbar);
-        setScrollbarNeedsPaintInvalidation(scrollbar);
-    }
-}
-
-void ScrollableArea::setScrollbarNeedsPaintInvalidation(Scrollbar* scrollbar)
+        scrollbar->invalidate();
+    }
+}
+
+void ScrollableArea::invalidateScrollbar(Scrollbar* scrollbar, const IntRect& rect)
 {
     if (scrollbar == horizontalScrollbar()) {
         if (GraphicsLayer* graphicsLayer = layerForHorizontalScrollbar()) {
@@ -412,8 +419,7 @@
             graphicsLayer->setContentsNeedsDisplay();
             return;
         }
-        m_horizontalScrollbarNeedsPaintInvalidation = true;
-        scrollControlWasSetNeedsPaintInvalidation();
+        invalidateScrollbarRect(scrollbar, rect);
         return;
     }
     if (scrollbar == verticalScrollbar()) {
@@ -422,22 +428,20 @@
             graphicsLayer->setContentsNeedsDisplay();
             return;
         }
-        m_verticalScrollbarNeedsPaintInvalidation = true;
-        scrollControlWasSetNeedsPaintInvalidation();
+        invalidateScrollbarRect(scrollbar, rect);
         return;
     }
     // Otherwise the scrollbar is just created and has not been set as either
     // horizontalScrollbar() or verticalScrollbar().
 }
 
-void ScrollableArea::setScrollCornerNeedsPaintInvalidation()
+void ScrollableArea::invalidateScrollCorner(const IntRect& rect)
 {
     if (GraphicsLayer* graphicsLayer = layerForScrollCorner()) {
         graphicsLayer->setNeedsDisplay();
         return;
     }
-    m_scrollCornerNeedsPaintInvalidation = true;
-    scrollControlWasSetNeedsPaintInvalidation();
+    invalidateScrollCornerRect(rect);
 }
 
 bool ScrollableArea::hasLayerForHorizontalScrollbar() const