Condense namespaces in tint/.

This PR condenses the namespaces in the tint/ folder.

Change-Id: Ia8d712f8c356b2714ebfa36443a4d78750293ce6
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/86039
Reviewed-by: Ben Clayton <bclayton@google.com>
Auto-Submit: Dan Sinclair <dsinclair@chromium.org>
Commit-Queue: Dan Sinclair <dsinclair@chromium.org>

src/tint/clone_context.h

@@ -28,16 +28,18 @@
 #include "src/tint/symbol.h"
 #include "src/tint/traits.h"
 
+// Forward declarations
+namespace tint::ast {
+class FunctionList;
+class Node;
+}  // namespace tint::ast
+
 namespace tint {
 
-// Forward declarations
+// Forward Declarations
 class CloneContext;
 class Program;
 class ProgramBuilder;
-namespace ast {
-class FunctionList;
-class Node;
-}  // namespace ast
 
 ProgramID ProgramIDOf(const Program*);
 ProgramID ProgramIDOf(const ProgramBuilder*);

src/tint/program.h

@@ -24,17 +24,16 @@
 #include "src/tint/sem/type_manager.h"
 #include "src/tint/symbol_table.h"
 
+// Forward Declarations
+namespace tint::ast {
+class Module;
+}  // namespace tint::ast
+
 namespace tint {
 
 // Forward declarations
 class CloneContext;
 
-namespace ast {
-
-class Module;
-
-}  // namespace ast
-
 /// Program holds the AST, Type information and SymbolTable for a tint program.
 class Program {
  public:

src/tint/program_builder.h

@@ -99,11 +99,9 @@
 #endif
 
 // Forward declarations
-namespace tint {
-namespace ast {
+namespace tint::ast {
 class VariableDeclStatement;
-}  // namespace ast
-}  // namespace tint
+}  // namespace tint::ast
 
 namespace tint {
 class CloneContext;

src/tint/traits_test.cc

@@ -16,8 +16,7 @@
 
 #include "gtest/gtest.h"
 
-namespace tint {
-namespace traits {
+namespace tint::traits {
 
 namespace {
 struct S {};
@@ -231,5 +230,4 @@ TEST(SliceTuple, MixedTupleSliceHighPart) {
   static_assert(std::is_same_v<std::tuple_element_t<1, sliced>, float>);
 }
 
-}  // namespace traits
-}  // namespace tint
+}  // namespace tint::traits