Fix overconstrained behaviour for position: sticky.

Source/core/rendering/RenderBoxModelObject.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2005 Allan Sandfeld Jensen (kde@carewolf.com)
  *           (C) 2005, 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2010 Google Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 301 matching lines @@
 
     if (containingBlock->hasOverflowClip()) {
         IntSize scrollOffset = containingBlock->layer()->scrollableArea()->adjustedScrollOffset();
         stickyLocation -= scrollOffset;
     }
 
     // We can't call localToAbsolute on |this| because that will recur. FIXME: For now, assume that |this| is not transformed.
     FloatRect absoluteStickyBoxRect(absContainerFrame.location() + stickyLocation, flippedStickyBoxRect.size());
     constraints.setAbsoluteStickyBoxRect(absoluteStickyBoxRect);
 
-    if (!style()->left().isAuto()) {
+    float horizontalOffsets = constraints.rightOffset() + constraints.leftOffset();
+    bool skipRight = false;
+    bool skipLeft = false;
+    if (!style()->left().isAuto() && !style()->right().isAuto()) {
+        if (horizontalOffsets > containerContentRect.width().toFloat()
+            || horizontalOffsets + containerContentRect.width().toFloat() > constrainingRect.width()) {
+            skipRight = style()->isLeftToRightDirection();
+            skipLeft = !skipRight;
+        }
+    }
+
+    if (!style()->left().isAuto() && !skipLeft) {
         constraints.setLeftOffset(floatValueForLength(style()->left(), constrainingRect.width()));
         constraints.addAnchorEdge(ViewportConstraints::AnchorEdgeLeft);
     }
 
-    if (!style()->right().isAuto()) {
+    if (!style()->right().isAuto() && !skipRight) {
         constraints.setRightOffset(floatValueForLength(style()->right(), constrainingRect.width()));
         constraints.addAnchorEdge(ViewportConstraints::AnchorEdgeRight);
     }
 
+    bool skipBottom = false;
+    // FIXME(ostap): Exclude top or bottom edge offset depending on the writing mode when related
+    // sections are fixed in spec: http://lists.w3.org/Archives/Public/www-style/2014May/0286.html
+    float verticalOffsets = constraints.topOffset() + constraints.bottomOffset();
+    if (!style()->top().isAuto() && !style()->bottom().isAuto()) {
+        if (verticalOffsets > containerContentRect.height().toFloat()
+            || verticalOffsets + containerContentRect.height().toFloat() > constrainingRect.height()) {
+            skipBottom = true;
+        }
+    }
+
     if (!style()->top().isAuto()) {
         constraints.setTopOffset(floatValueForLength(style()->top(), constrainingRect.height()));
         constraints.addAnchorEdge(ViewportConstraints::AnchorEdgeTop);
     }
 
-    if (!style()->bottom().isAuto()) {
-        constraints.setBottomOffset(floatValueForLength(style()->bottom(), constrainingRect.height() ));
+    if (!style()->bottom().isAuto() && !skipBottom) {
+        constraints.setBottomOffset(floatValueForLength(style()->bottom(), constrainingRect.height()));
         constraints.addAnchorEdge(ViewportConstraints::AnchorEdgeBottom);
     }
 }
 
 LayoutSize RenderBoxModelObject::stickyPositionOffset() const
 {
     FloatRect constrainingRect;
 
     ASSERT(hasLayer());
     RenderLayer* enclosingClippingLayer = layer()->enclosingOverflowClipLayer(ExcludeSelf);
@@ skipping 2475 matching lines @@
     ASSERT(!beforeChild || toBoxModelObject == beforeChild->parent());
     for (RenderObject* child = startChild; child && child != endChild; ) {
         // Save our next sibling as moveChildTo will clear it.
         RenderObject* nextSibling = child->nextSibling();
         moveChildTo(toBoxModelObject, child, beforeChild, fullRemoveInsert);
         child = nextSibling;
     }
 }
 
 } // namespace WebCore