Update return value of getComputedStyle for sticky elements

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 9d4e5c14c0e8de4d66f367f8eff7ae977eaba06c..b65057c8393f3e3097efb039bcb3b3696f975d40 100644
--- a/third_party/WebKit/Source/core/css/ComputedStyleCSSValueMapping.cpp
+++ b/third_party/WebKit/Source/core/css/ComputedStyleCSSValueMapping.cpp
@@ -222,9 +222,15 @@ static CSSValue* ValueForPositionOffset(const ComputedStyle& style,
   }
 
   if (offset.IsAuto() && layout_object) {
+    // "top:auto" and "top:0px" have very different meaning for sticky elements.
+    // Therefore "auto" should be returned regardless the opposite.
+    // https://crbug.com/703816.
+    if (layout_object->IsStickyPositioned())
+      return CSSIdentifierValue::Create(CSSValueAuto);

[flackr, 2017/05/09 20:45:52]

This extra condition should no longer be necessary given the change on 227
right?

[yigu, 2017/05/09 21:08:06]

Yes. Done.

+
     // If the property applies to a positioned element and the resolved value of
     // the display property is not none, the resolved value is the used value.
-    if (layout_object->IsInFlowPositioned()) {
+    if (layout_object->IsRelPositioned()) {
       // If e.g. left is auto and right is not auto, then left's computed value
       // is negative right. So we get the opposite length unit and see if it is
       // auto.