[tint] Pass Program by reference, not pointer.

Also use references in fields, where possible.

Bug: tint:1698
Change-Id: I61e42df007ab233cef841fef2d646653ed190893
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/152545
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
diff --git a/src/tint/lang/wgsl/program/program_builder_test.cc b/src/tint/lang/wgsl/program/program_builder_test.cc
index b887ff6..c1c3099 100644
--- a/src/tint/lang/wgsl/program/program_builder_test.cc
+++ b/src/tint/lang/wgsl/program/program_builder_test.cc
@@ -42,7 +42,7 @@
     ASSERT_TRUE(inner.Symbols().Get("a").IsValid());
     ASSERT_FALSE(inner.Symbols().Get("b").IsValid());
 
-    ProgramBuilder outer = ProgramBuilder::Wrap(&inner);
+    ProgramBuilder outer = ProgramBuilder::Wrap(inner);
 
     ASSERT_EQ(inner.AST().Functions().Length(), 1u);
     ASSERT_EQ(outer.AST().Functions().Length(), 1u);