[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 0135ce998a063489d836b0ed852b032a89873fae..767f119ec67ca4f864ffc3b0ed130206470958bd 100644
--- a/Source/core/css/resolver/StyleBuilderCustom.cpp
+++ b/Source/core/css/resolver/StyleBuilderCustom.cpp
@@ -1004,6 +1004,9 @@ 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;
         }