Bug 1270891 - Don't honor forced break properties when generating flex lines. r=dholbert

This behavior was based on the old spec. See the spec changes in
https://drafts.csswg.org/css-flexbox-1/#change-201409-algo-breaks

Differential Revision: https://phabricator.services.mozilla.com/D172697

layout/generic/nsFlexContainerFrame.cpp

@@ -3964,7 +3964,6 @@ void nsFlexContainerFrame::GenerateFlexLines(
   AddOrRemoveStateBits(NS_STATE_FLEX_NORMAL_FLOW_CHILDREN_IN_CSS_ORDER,
                        iter.ItemsAreAlreadyInOrder());
 
-  bool prevItemRequestedBreakAfter = false;
   const bool useMozBoxCollapseBehavior =
       StyleVisibility()->UseLegacyCollapseBehavior();
 
@@ -3976,15 +3975,6 @@ void nsFlexContainerFrame::GenerateFlexLines(
       continue;
     }
 
-    // If we're multi-line and current line isn't empty, create a new flex line
-    // to satisfy the previous flex item's request or to honor "break-before".
-    if (!isSingleLine && !curLine->IsEmpty() &&
-        (prevItemRequestedBreakAfter ||
-         childFrame->StyleDisplay()->BreakBefore())) {
-      curLine = ConstructNewFlexLine();
-      prevItemRequestedBreakAfter = false;
-    }
-
     const bool collapsed = childFrame->StyleVisibility()->IsCollapse();
     aHasCollapsedItems = aHasCollapsedItems || collapsed;
 
@@ -4034,12 +4024,6 @@ void nsFlexContainerFrame::GenerateFlexLines(
 
     // Update the line's bookkeeping about how large its items collectively are.
     curLine->AddLastItemToMainSizeTotals();
-
-    // Honor "break-after" if we're multi-line. If we have more children, we
-    // will create a new flex line in the next iteration.
-    if (!isSingleLine && childFrame->StyleDisplay()->BreakAfter()) {
-      prevItemRequestedBreakAfter = true;
-    }
     itemIdxInContainer++;
   }
 }

testing/web-platform/meta/css/css-flexbox/flexbox-break-request-horiz-001a.html.ini

@@ -1,2 +0,0 @@
-[flexbox-break-request-horiz-001a.html]
-  expected: FAIL

testing/web-platform/meta/css/css-flexbox/flexbox-break-request-horiz-001b.html.ini

@@ -1,2 +0,0 @@
-[flexbox-break-request-horiz-001b.html]
-  expected: FAIL

testing/web-platform/meta/css/css-flexbox/flexbox-break-request-vert-001a.html.ini

@@ -1,2 +0,0 @@
-[flexbox-break-request-vert-001a.html]
-  expected: FAIL

testing/web-platform/meta/css/css-flexbox/flexbox-break-request-vert-001b.html.ini

@@ -1,2 +0,0 @@
-[flexbox-break-request-vert-001b.html]
-  expected: FAIL