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..02c3a79f8461dcb21b43590fe08566371b6d850a 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 (!offset.isAuto() && layoutObject->isInFlowPositioned()) {

[rune, 2016/05/18 21:41:07]

offset is not auto at this point, so no need to check it. Did you mean to check
opposite here?

[Deokjin Kim, 2016/05/18 23:29:55]

You're right. It's typo. I intended to use opposite, not offset.

[mstensho (USE GERRIT), 2016/05/19 05:57:52]

No tests failed because of the typo? Then I think we need another test.

[Deokjin Kim, 2016/05/19 12:57:24]

I added 1 more test
case(fast/css/getComputedStyle/getComputedStyle-right-auto.html). With checking
offset, this is failed. But with checking opposite, this is passed.

+            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);
 }