[CSS Grid Layout] Add support to place items using named grid lines

Source/core/css/resolver/StyleBuilderCustom.cpp

Index: Source/core/css/resolver/StyleBuilderCustom.cpp
diff --git a/Source/core/css/resolver/StyleBuilderCustom.cpp b/Source/core/css/resolver/StyleBuilderCustom.cpp
index 1a5623e5efe9147ba36642c9dcc0f84837270c36..79670c24ed9777b32ee5322ba51ae35835d3bcf7 100644
--- a/Source/core/css/resolver/StyleBuilderCustom.cpp
+++ b/Source/core/css/resolver/StyleBuilderCustom.cpp
@@ -966,6 +966,9 @@ static bool createGridPosition(CSSValue* value, GridPosition& position)
         // We translate <ident> to <string> during parsing as it
         // makes handling it more simple.
         if (primitiveValue->isString()) {
+            // Note that a <ident> could be either a grid area or a grid line name. We create them as grid areas but the
+            // StyleAdjuster will have to check if this is the name of a grid area, the name of a grid line or the
+            // prefix of a grid line named <ident>-start or <ident>-end.
             position.setNamedGridArea(primitiveValue->getStringValue());
             return true;
         }