Enable position:sticky for <thead> and <tr> elements

third_party/WebKit/Source/core/css/resolver/StyleAdjuster.cpp

Index: third_party/WebKit/Source/core/css/resolver/StyleAdjuster.cpp
diff --git a/third_party/WebKit/Source/core/css/resolver/StyleAdjuster.cpp b/third_party/WebKit/Source/core/css/resolver/StyleAdjuster.cpp
index 24af17b064d28bd633f3238410a162b668816594..d68021731f6653dd795ef0136abb84553abdeef0 100644
--- a/third_party/WebKit/Source/core/css/resolver/StyleAdjuster.cpp
+++ b/third_party/WebKit/Source/core/css/resolver/StyleAdjuster.cpp
@@ -340,16 +340,14 @@ static void adjustStyleForDisplay(ComputedStyle& style,
       style.getWritingMode() != layoutParentStyle.getWritingMode())
     style.setDisplay(EDisplay::kInlineBlock);
 
-  // We do not honor position: relative or sticky for table rows, headers, and
-  // footers. This is correct for position: relative in CSS2.1 (and caused a
-  // crash in containingBlock() on some sites) and position: sticky is defined
-  // as following position: relative behavior for table elements. It is
-  // incorrect for CSS3.
+  // We do not honor position: relative for table rows, headers, and footers.
+  // This is correct for CSS2.1 (and honoring it caused a crash in
+  // containingBlock() on some sites). It is incorrect for CSS3.
   if ((style.display() == EDisplay::kTableHeaderGroup ||
        style.display() == EDisplay::kTableRowGroup ||
        style.display() == EDisplay::kTableFooterGroup ||
        style.display() == EDisplay::kTableRow) &&
-      style.hasInFlowPosition())
+      style.position() == EPosition::kRelative)

[mstensho (USE GERRIT), 2017/03/29 18:27:55]

This change will let e.g. a table-row act as a containing block for absolutely
positioned descendants. I cannot imagine that it will work out of the box.

<div style="display:table-row; position:sticky;">
    <div style="position:absolute;"></div>
</div>

     style.setPosition(EPosition::kStatic);
 
   // Cannot support position: sticky for table columns and column groups because