Adapt and reland old position sticky implementation

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 cffe90e1a6a699f5bde5aa09d48f237edde15443..d796adeb53bf07c6d33df623dab6de6f457ae27e 100644
--- a/third_party/WebKit/Source/core/css/resolver/StyleAdjuster.cpp
+++ b/third_party/WebKit/Source/core/css/resolver/StyleAdjuster.cpp
@@ -197,7 +197,7 @@ void StyleAdjuster::adjustComputedStyle(ComputedStyle& style, const ComputedStyl
         || style.hasFilter()
         || style.hasBlendMode()
         || style.hasIsolation()
-        || style.position() == FixedPosition
+        || style.hasViewportConstrainedPosition()
         || isInTopLayer(e, style)
         || hasWillChangeThatCreatesStackingContext(style)))
         style.setZIndex(0);
@@ -464,6 +464,12 @@ void StyleAdjuster::adjustStyleForDisplay(ComputedStyle& style, const ComputedSt
         && style.position() == RelativePosition)
         style.setPosition(StaticPosition);
 
+    // Cannot support position: sticky for table columns and column groups because current code is only doing
+    // background painting through columns / column groups

[chrishtr, 2015/10/06 17:08:33]

Is this recorded in a bug?

According to this spec:

https://drafts.csswg.org/css-position-3/#valdef-position-sticky

position: sticky is not supposed to apply to any table elements.

[flackr, 2015/10/07 20:38:12]

Hmm, doesn't look like it, just the bug for a crash allowing sticky in this
context used to cause. See the original review:
https://codereview.chromium.org/196413002/

According to https://bugs.webkit.org/show_bug.cgi?id=112024 table rows should be
able to stick. Perhaps I'm mistaken, but my reading of the spec was that for
table elements it should have the same ability to "offset" as relative does
(https://drafts.csswg.org/css-position-3/#valdef-position-relative) - which I
thought meant that columns and column groups will not be offset but rows and row
groups can be offset. There are even a couple tests for this:
fast/css/sticky/sticky-table-row-top.html
fast/css/sticky/sticky-table-thead-top.html 

It is strange that this doesn't seem to be consistent with the code above which
suggests that header groups, row groups, footer groups and rows do not offset.
It also looks like there are known bugs with table rows being absolute position
containing blocks (http://crbug.com/443190)...

[chrishtr, 2015/11/04 01:40:43]

The spec says: "The effect of position: sticky on table elements is the same as
for position: relative". Doesn't that mean that table elements can't be sticky?

As crbug.com/443190 indicates (I duped it into another bug BTW), tables are
special and some of the subclasses can't be containing
blocks in our current implementation. This may actually be a constraint of the
way they are spec'ed, I never got to the bottom of looking into that.

See https://code.google.com/p/chromium/issues/detail?id=477495#c9

I think we should likely only support sticky for LayoutTable, but not any of the
other table-related classes. Maybe also LayoutTableCell?

It appears the lines in this function implement that restriction? Please confirm
and add a comment explaining.

[flackr, 2015/11/25 21:03:01]

There are many public examples where sticky is used on a table row to produce an
always visible table header. I do believe it is intended to work on table rows.

Under position: relative on
https://drafts.csswg.org/css-position/#valdef-position-relative it says that
only table-column-group and table-column do not offset.

+    if ((style.display() == TABLE_COLUMN_GROUP || style.display() == TABLE_COLUMN)
+        && style.position() == StickyPosition)
+        style.setPosition(StaticPosition);
+
     // writing-mode does not apply to table row groups, table column groups, table rows, and table columns.
     // FIXME: Table cells should be allowed to be perpendicular or flipped with respect to the table, though.
     if (style.display() == TABLE_COLUMN || style.display() == TABLE_COLUMN_GROUP || style.display() == TABLE_FOOTER_GROUP