Condense namespaces in tint/transform.

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

Change-Id: Idf448870ccf90f892b9186f7aab7bb0ac9deda17
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/86029
Auto-Submit: Dan Sinclair <dsinclair@chromium.org>
Reviewed-by: Ben Clayton <bclayton@google.com>
Commit-Queue: Dan Sinclair <dsinclair@chromium.org>
diff --git a/src/tint/transform/expand_compound_assignment.cc b/src/tint/transform/expand_compound_assignment.cc
index 3a986a2..0473fae 100644
--- a/src/tint/transform/expand_compound_assignment.cc
+++ b/src/tint/transform/expand_compound_assignment.cc
@@ -27,8 +27,7 @@
 
 TINT_INSTANTIATE_TYPEINFO(tint::transform::ExpandCompoundAssignment);
 
-namespace tint {
-namespace transform {
+namespace tint::transform {
 
 ExpandCompoundAssignment::ExpandCompoundAssignment() = default;
 
@@ -192,5 +191,4 @@
   state.Finalize();
 }
 
-}  // namespace transform
-}  // namespace tint
+}  // namespace tint::transform