Fix some tests that were broken in the library tag removal.

Closes #1382

R=rnystrom@google.com

Review URL: https://codereview.chromium.org//1590723005 .

test/dart2js/allows_import_in_dart_code_test.dart

@@ -14,6 +14,7 @@ main() {
       d.libPubspec("foo", "0.0.1"),
       d.dir("lib", [
         d.file("foo.dart", """
+foo() => 'footext';
 """)
       ])
     ]).create();
@@ -24,6 +25,7 @@ main() {
       }),
       d.dir("lib", [
         d.file("lib.dart", """
+lib() => 'libtext';
 """)
       ]),
       d.dir("web", [

test/dart2js/compiles_generated_file_from_dependency_outside_web_test.dart

@@ -30,6 +30,7 @@ import "other.dart";
 void main() => print(TOKEN);
 """),
         d.file("other.dart", """
+const TOKEN = "before";
 """)
       ])
     ]).create();

test/dart2js/compiles_generated_file_from_dependency_test.dart

@@ -22,6 +22,7 @@ main() {
       }),
       d.dir("lib", [
         d.file("foo.dart", """
+const TOKEN = "before";
 foo() => TOKEN;
 """),
         d.file("transformer.dart", dartTransformer("munge"))

test/dart2js/compiles_imported_generated_file_test.dart

@@ -28,6 +28,7 @@ import "other.dart";
 void main() => print(TOKEN);
 """),
         d.file("other.dart", """
+const TOKEN = "before";
 """)
       ])
     ]).create();