getComputedStyle should handle over-constrained properties.

third_party/WebKit/Source/core/css/ComputedStyleCSSValueMapping.cpp

Index: third_party/WebKit/Source/core/css/ComputedStyleCSSValueMapping.cpp
diff --git a/third_party/WebKit/Source/core/css/ComputedStyleCSSValueMapping.cpp b/third_party/WebKit/Source/core/css/ComputedStyleCSSValueMapping.cpp
index 6f6d9465840e73bf9bd1165904ccfc566da9bce8..56813871afa728e1882bfb1d086ebab88f429e4c 100644
--- a/third_party/WebKit/Source/core/css/ComputedStyleCSSValueMapping.cpp
+++ b/third_party/WebKit/Source/core/css/ComputedStyleCSSValueMapping.cpp
@@ -247,6 +247,14 @@ static CSSValue* valueForPositionOffset(const ComputedStyle& style, CSSPropertyI
     if (offset.isAuto())
         return cssValuePool().createIdentifierValue(CSSValueAuto);
 
+    if (layoutObject) {
+        if (!opposite.isAuto() && layoutObject->isInFlowPositioned()) {
+            LayoutBlock* container = layoutObject->containingBlock();
+            bool ltr = container->style()->isLeftToRightDirection();
+            if ((propertyID == CSSPropertyLeft && !ltr) || (propertyID == CSSPropertyRight && ltr) || (propertyID == CSSPropertyBottom))
+                return zoomAdjustedPixelValue(-opposite.pixels(), style);
+        }
+    }
     return zoomAdjustedPixelValueForLength(offset, style);
 }