[CSS Grid Layout] Support sparse in auto-placement algorithm

LayoutTests/fast/css-grid-layout/grid-item-auto-placement-automatic-span.html

Index: LayoutTests/fast/css-grid-layout/grid-item-auto-placement-automatic-span.html
diff --git a/LayoutTests/fast/css-grid-layout/grid-item-auto-placement-automatic-span.html b/LayoutTests/fast/css-grid-layout/grid-item-auto-placement-automatic-span.html
index f8e96c3f25a23ce140cf20d7d0e012bc02aba119..930bbde0a20969c9dbf312b850fa1a1ff43a5518 100644
--- a/LayoutTests/fast/css-grid-layout/grid-item-auto-placement-automatic-span.html
+++ b/LayoutTests/fast/css-grid-layout/grid-item-auto-placement-automatic-span.html
@@ -15,12 +15,6 @@
     grid-template-rows: 50px 100px (line) 200px (line);
 }
 
-.autoRowAutoColumnSpanning2 {
-    background-color: maroon;
-    grid-column: span 2;
-    grid-row: auto;
-}
-
 .autoRowAutoColumnSpanning3 {
     background-color: teal;
     grid-column: span 3;
@@ -91,7 +85,7 @@
 </div>
 
 <div style="position: relative">
-    <div class="grid gridAutoFlowRow">
+    <div class="grid gridAutoFlowRowDense">
         <div class="sizedToGridArea autoRowFirstColumn" data-offset-x="0" data-offset-y="0" data-expected-width="100" data-expected-height="50"></div>
         <div class="sizedToGridArea autoRowSecondColumn" data-offset-x="100" data-offset-y="0" data-expected-width="100" data-expected-height="50"></div>
         <div class="sizedToGridArea autoRowThirdColumn" data-offset-x="200" data-offset-y="0" data-expected-width="100" data-expected-height="50"></div>
@@ -119,7 +113,7 @@
 </div>
 
 <div style="position: relative">
-    <div class="grid gridAutoFlowRow gridNamedGridLinesColumns">
+    <div class="grid gridAutoFlowRowDense gridNamedGridLinesColumns">
         <div class="sizedToGridArea autoRowFirstColumn" data-offset-x="0" data-offset-y="0" data-expected-width="50" data-expected-height="50"></div>
         <div class="sizedToGridArea autoRowAutoColumnSpanning2Line" data-offset-x="50" data-offset-y="0" data-expected-width="100" data-expected-height="50"></div>
         <div class="sizedToGridArea autoRowSecondColumn" data-offset-x="50" data-offset-y="50" data-expected-width="100" data-expected-height="50"></div>
@@ -152,7 +146,7 @@
 </div>
 
 <div style="position: relative">
-    <div class="grid gridAutoFlowColumn">
+    <div class="grid gridAutoFlowColumnDense">
         <div class="sizedToGridArea firstRowAutoColumn" data-offset-x="0" data-offset-y="0" data-expected-width="100" data-expected-height="50"></div>
         <div class="sizedToGridArea secondRowAutoColumn" data-offset-x="0" data-offset-y="50" data-expected-width="100" data-expected-height="50"></div>
         <div class="sizedToGridArea thirdRowAutoColumn" data-offset-x="0" data-offset-y="100" data-expected-width="100" data-expected-height="50"></div>
@@ -180,7 +174,7 @@
 </div>
 
 <div style="position: relative">
-    <div class="grid gridAutoFlowColumn gridNamedGridLinesRows">
+    <div class="grid gridAutoFlowColumnDense gridNamedGridLinesRows">
         <div class="sizedToGridArea firstRowAutoColumn" data-offset-x="0" data-offset-y="0" data-expected-width="100" data-expected-height="50"></div>
         <div class="sizedToGridArea autoRowSpanning2LineAutoColumn" data-offset-x="0" data-offset-y="50" data-expected-width="100" data-expected-height="100"></div>
         <div class="sizedToGridArea secondRowAutoColumn" data-offset-x="100" data-offset-y="50" data-expected-width="100" data-expected-height="100"></div>