Add LocationDecoration ToStr test.

Bug: tint:11
Change-Id: I8327d2f3961e4d8d74c6339b66ba36218126e63e
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/16562
Reviewed-by: Sarah Mashayekhi <sarahmashay@google.com>
diff --git a/src/ast/kill_statement_test.cc b/src/ast/kill_statement_test.cc
index 35e1b37..63115c7 100644
--- a/src/ast/kill_statement_test.cc
+++ b/src/ast/kill_statement_test.cc
@@ -55,4 +55,3 @@
 
 }  // namespace ast
 }  // namespace tint
-
diff --git a/src/ast/location_decoration_test.cc b/src/ast/location_decoration_test.cc
index 7858193..c68253a 100644
--- a/src/ast/location_decoration_test.cc
+++ b/src/ast/location_decoration_test.cc
@@ -14,6 +14,8 @@
 
 #include "src/ast/location_decoration.h"
 
+#include <sstream>
+
 #include "gtest/gtest.h"
 
 namespace tint {
@@ -34,5 +36,13 @@
   EXPECT_FALSE(d.IsSet());
 }
 
+TEST_F(LocationDecorationTest, ToStr) {
+  LocationDecoration d{2};
+  std::ostringstream out;
+  d.to_str(out);
+  EXPECT_EQ(out.str(), R"(LocationDecoration{2}
+)");
+}
+
 }  // namespace ast
 }  // namespace tint