Add Convert/Make factory functions to IndexExpression.

Change-Id: I7a7874e58bf53978afce8a41b26092406b6490ed
Bug: skia:11342
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/380360
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
diff --git a/src/sksl/SkSLInliner.cpp b/src/sksl/SkSLInliner.cpp
index 4c16b93..6d32357 100644
--- a/src/sksl/SkSLInliner.cpp
+++ b/src/sksl/SkSLInliner.cpp
@@ -358,8 +358,7 @@
             return expression.clone();
         case Expression::Kind::kIndex: {
             const IndexExpression& idx = expression.as<IndexExpression>();
-            return std::make_unique<IndexExpression>(*fContext, expr(idx.base()),
-                                                     expr(idx.index()));
+            return IndexExpression::Make(*fContext, expr(idx.base()), expr(idx.index()));
         }
         case Expression::Kind::kPrefix: {
             const PrefixExpression& p = expression.as<PrefixExpression>();