[CSS Grid Layout] Flex tracks sizing alg must handle 0fr values

LayoutTests/fast/css-grid-layout/flex-factor-sum-less-than-1.html

Index: LayoutTests/fast/css-grid-layout/flex-factor-sum-less-than-1.html
diff --git a/LayoutTests/fast/css-grid-layout/flex-factor-sum-less-than-1.html b/LayoutTests/fast/css-grid-layout/flex-factor-sum-less-than-1.html
index d8cf2ed18ee557f5ce09950c5652c69b22c18492..f9fd9b19e7b5f9908ec004dd2a14200a082faf43 100644
--- a/LayoutTests/fast/css-grid-layout/flex-factor-sum-less-than-1.html
+++ b/LayoutTests/fast/css-grid-layout/flex-factor-sum-less-than-1.html
@@ -19,6 +19,11 @@
     width: 100px;
     height: 100px;
 }
+.zeroValueFlexFactor {
+    grid-template-columns: .0fr .2fr .3fr;
+    grid-template-rows: 50px;
+    width: 100px;
+}
 .firstRowThirdColumn {
     background-color: yellow;
     grid-column: 3;
@@ -62,6 +67,14 @@
 </div>
 
 <div style="position: relative;">
+    <div class="grid zeroValueFlexFactor">
+        <div class="firstRowFirstColumn" data-expected-width="0" data-expected-height="50"></div>
+        <div class="firstRowSecondColumn" data-expected-width="20" data-expected-height="50"></div>
+        <div class="firstRowThirdColumn" data-expected-width="30" data-expected-height="50"></div>
+    </div>
+</div>
+
+<div style="position: relative;">
     <div class="grid fixedAndfractionFlexFactors">
         <div class="firstRowFirstColumn" data-expected-width="50" data-expected-height="5"></div>
         <div class="firstRowSecondColumn" data-expected-width="4" data-expected-height="5"></div>