Bug 1540220 - Remove some useless usage of LazyComputeBehavior::Allow. r=dholbert

This switches nsFrameSetFrame's hacky frame construction codepath to operate on
the flattened tree, since it made me a bit more comfortable about it (all layout
should operate on is the flattened tree, though in this cause this should not
cause any web-observable behavior change, since  can't be a shadow
host per spec, and we no longer support XBL-in-content).

That doesn't need to compute styles lazily. You only need to compute styles
lazily in descendants of display: none elements, and even though this code
doesn't check on display: none _on the children_, the parent element should
never have display: none (since we're creating an nsFrameSetFrame for it).

There are other places that still call into this (apart from getComputedStyle).

One is nsImageFrame's cursor code. Given the  elements referencing an
image map could be anywhere, we need to have lazy computation here.

The other is the viewport style propagation stuff. There shouldn't be a need for
LazyComputeBehavior::Allow on the document element in order to check the
viewport styles propagation, since the root element can't have display: none
ancestors. But we run that code before actually constructing the doc element
containing block, which is when we do the initial document styling.

We could remove that with some more effort, but it's not worth it right now,
since we need to keep using it for the , since the document element could
be display: none itself, and we propagate the overflow styles in that case
still. I filed w3c/csswg-drafts#3779 to potentially
change that.

Differential Revision: https://phabricator.services.mozilla.com/D25455

UltraBlame original commit: ae9783be99324502017f3c9bfc92cb811fd1993e

Author: marco-c

layout/generic/nsFrameSetFrame.cpp

@@ -353,6 +353,17 @@ mozilla
 /
 dom
 /
+ChildIterator
+.
+h
+"
+#
+include
+"
+mozilla
+/
+dom
+/
 HTMLFrameSetElement
 .
 h
@@ -2161,27 +2172,31 @@ or
 frameset
 >
 children
+FlattenedChildIterator
+children
+(
+mContent
+)
+;
 for
 (
 nsIContent
 *
 child
 =
-mContent
--
->
-GetFirstChild
+children
+.
+GetNextChild
 (
 )
 ;
 child
 ;
 child
 =
-child
--
->
-GetNextSibling
+children
+.
+GetNextChild
 (
 )
 )
@@ -2298,20 +2313,6 @@ if
 child
 -
 >
-IsHTMLElement
-(
-)
-)
-{
-continue
-;
-}
-if
-(
-!
-child
--
->
 IsAnyOfHTMLElements
 (
 nsGkAtoms
@@ -2328,11 +2329,48 @@ frame
 continue
 ;
 }
+/
+/
+FIXME
+(
+emilio
+)
+:
+This
+doesn
+'
+t
+even
+respect
+display
+:
+none
+but
+that
+matches
+/
+/
+other
+browsers
+;
+_
+;
+/
+/
+/
+/
+Maybe
+we
+should
+change
+that
+though
+.
 RefPtr
 <
 ComputedStyle
 >
-kidSC
+kidStyle
 =
 presShell
 -
@@ -2342,18 +2380,15 @@ StyleSet
 )
 -
 >
-ResolveStyleFor
+ResolveServoStyle
 (
+*
 child
 -
 >
 AsElement
 (
 )
-LazyComputeBehavior
-:
-:
-Allow
 )
 ;
 nsIFrame
@@ -2379,7 +2414,7 @@ frame
 NS_NewHTMLFramesetFrame
 (
 presShell
-kidSC
+kidStyle
 )
 ;
 nsHTMLFramesetFrame
@@ -2452,7 +2487,7 @@ frame
 NS_NewSubDocumentFrame
 (
 presShell
-kidSC
+kidStyle
 )
 ;
 frame