go/types: some prep work for making `import "chans"` (testdata/map.go2) work

To make the import work, the import needs to be changed into
`import "./chan"`, the file testdata/chans.go2 needs to be
copies into a new directory testdata/chan and the file must
be renamed to chans.go.

But this exposes some problem with instantiating parameterized
types with other type parameters. Delaying this for now.

Change-Id: I1cd784fb89c2374131f3b1105493492eb0189abc

src/go/types/check_test.go

@@ -275,7 +275,9 @@ func checkFiles(t *testing.T, testfiles []string) {
 		conf.FakeImportC = true
 	}
 	conf.Trace = testing.Verbose()
-	conf.Importer = importer.Default()
+	// We don't use importer.Default() below so we can eventually
+	// get testdata/map.go2 to import chans (still to be fixed).
+	conf.Importer = importer.ForCompiler(fset, "source", nil)
 	conf.Error = func(err error) {
 		if *haltOnError {
 			defer panic(err)

src/go/types/testdata/map.go2

@@ -89,8 +89,8 @@ func (m *Map(K, V)) InOrder() *Iterator(K, V) {
 		f(m.root)
 		sender.Close()
 	}()
-	// TODO(gri) The design doc doensn't require that we repeat the
-	// type parameters here. Fix the implementation.
+	// TODO(gri) The design draft doesn't require that we repeat
+	// the type parameters here. Fix the implementation.
 	return &Iterator(K, V){receiver}
 	// return &Iterator{receiver}
 }