[LayoutNG] Don't combine exclusions on a node if its desendants have some

If the descendants of an opportunity tree node have exclusions they will
get lost when combining the node's current exclusions, so avoid doing that.

Bug: 798436
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_layout_tests_layout_ng
Change-Id: I90cde607c99fcfc808c1dafc531445bc25774cca
Reviewed-on: https://chromium-review.googlesource.com/847595Reviewed-by: Emil A Eklund <eae@chromium.org>
Commit-Queue: Emil A Eklund <eae@chromium.org>
Cr-Commit-Position: refs/heads/master@{#526554}

third_party/WebKit/LayoutTests/FlagExpectations/enable-blink-features=LayoutNG

@@ -3424,7 +3424,6 @@ crbug.com/591099 fast/block/child-not-removed-from-parent-lineboxes-crash.html [
 crbug.com/591099 fast/block/containing-block-negative-margins.html [ Failure ]
 crbug.com/591099 fast/block/float-avoids-padding-inline-ancestors.html [ Crash ]
 crbug.com/591099 fast/block/float/003.html [ Failure ]
-crbug.com/591099 fast/block/float/010.html [ Failure ]
 crbug.com/714962 fast/block/float/015.html [ Failure ]
 crbug.com/591099 fast/block/float/018.html [ Failure ]
 crbug.com/714962 fast/block/float/021.html [ Failure ]

third_party/WebKit/Source/core/layout/ng/ng_layout_opportunity_iterator.cc

@@ -187,6 +187,16 @@ NGLayoutOpportunity GetTopSpace(const NGLayoutOpportunity& parent_opportunity,
   return NGLayoutOpportunity();
 }
 
+bool CanCombineExclusions(NGLayoutOpportunityTreeNode* node) {
+  if (node->left && node->left->combined_exclusion)
+    return false;
+  if (node->right && node->right->combined_exclusion)
+    return false;
+  if (node->bottom && node->bottom->combined_exclusion)
+    return false;
+  return true;
+}
+
 // Inserts the exclusion into the Layout Opportunity tree.
 void InsertExclusion(NGLayoutOpportunityTreeNode* node,
                      const NGExclusion* exclusion,
@@ -218,7 +228,8 @@ void InsertExclusion(NGLayoutOpportunityTreeNode* node,
 
   DCHECK(!node->exclusions.IsEmpty());
 
-  if (node->combined_exclusion->MaybeCombineWith(*exclusion)) {
+  if (CanCombineExclusions(node) &&
+      node->combined_exclusion->MaybeCombineWith(*exclusion)) {
     SplitNGLayoutOpportunityTreeNode(node->combined_exclusion->rect, node);
     node->exclusions.push_back(exclusion);
   } else {