wsgl parser: Tweak top-level unexpected token error message

I feel this reads better.

Bug: tint:282
Change-Id: I04fe42a0347ea050e93e5cf5ccae7259bc79bb58
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/32283
Commit-Queue: dan sinclair <dsinclair@chromium.org>
Reviewed-by: dan sinclair <dsinclair@chromium.org>

src/reader/wgsl/parser_impl.cc

diff --git a/src/reader/wgsl/parser_impl.cc b/src/reader/wgsl/parser_impl.cc
index ea0b5ae..01d3678 100644
--- a/src/reader/wgsl/parser_impl.cc
+++ b/src/reader/wgsl/parser_impl.cc
@@ -286,7 +286,7 @@
   if (decos.value.size() > 0) {
     add_error(peek(), "expected declaration after decorations");
   } else {
-    add_error(peek(), "invalid token");
+    add_error(peek(), "unexpected token");
   }
   return Failure::kErrored;
 }

src/reader/wgsl/parser_impl_error_msg_test.cc

diff --git a/src/reader/wgsl/parser_impl_error_msg_test.cc b/src/reader/wgsl/parser_impl_error_msg_test.cc
index e72a80e..3d70cd9 100644
--- a/src/reader/wgsl/parser_impl_error_msg_test.cc
+++ b/src/reader/wgsl/parser_impl_error_msg_test.cc
@@ -1262,7 +1262,7 @@
 
 TEST_F(ParserImplErrorTest, UnexpectedToken) {
   EXPECT("unexpected",
-         "test.wgsl:1:1 error: invalid token\n"
+         "test.wgsl:1:1 error: unexpected token\n"
          "unexpected\n"
          "^^^^^^^^^^\n");
 }