Condense namespaces in tint/ast.

This PR condenses the namespaces in the tint/ast folder.

Change-Id: I77a84fb03f921b4db7135572005a08563f2fb60b
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/86038
Reviewed-by: Ben Clayton <bclayton@google.com>
Auto-Submit: Dan Sinclair <dsinclair@chromium.org>
Commit-Queue: Dan Sinclair <dsinclair@chromium.org>
diff --git a/src/tint/ast/int_literal_expression.h b/src/tint/ast/int_literal_expression.h
index 9da44bb..9ca3105 100644
--- a/src/tint/ast/int_literal_expression.h
+++ b/src/tint/ast/int_literal_expression.h
@@ -17,8 +17,7 @@
 
 #include "src/tint/ast/literal_expression.h"
 
-namespace tint {
-namespace ast {
+namespace tint::ast {
 
 /// An integer literal. This could be either signed or unsigned.
 class IntLiteralExpression
@@ -39,7 +38,6 @@
   IntLiteralExpression(ProgramID pid, const Source& src);
 };  // namespace ast
 
-}  // namespace ast
-}  // namespace tint
+}  // namespace tint::ast
 
 #endif  // SRC_TINT_AST_INT_LITERAL_EXPRESSION_H_