cmd/go: set DepOnly on package when calling go list -deps

Currently .DepOnly is set when go list -test is invoked to help
distinguish those packages that matched the command line spec from those
which are dependencies (of test packages). This is also useful when
calling go list -deps for the same reason.

Change-Id: Ifc0e68dad0fd01355928793ef803691dee5f4f29
Reviewed-on: https://go-review.googlesource.com/112755
Run-TryBot: Paul Jolly <paul@myitcv.org.uk>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Russ Cox <rsc@golang.org>

src/cmd/go/go_test.go

@@ -1975,6 +1975,10 @@ func TestGoListTest(t *testing.T) {
 
 	tg.run("list", "-test", "runtime/cgo")
 	tg.grepStdout(`^runtime/cgo$`, "missing runtime/cgo")
+
+	tg.run("list", "-deps", "-f", "{{if .DepOnly}}{{.ImportPath}}{{end}}", "sort")
+	tg.grepStdout(`^reflect$`, "missing reflect")
+	tg.grepStdoutNot(`^sort`, "unexpected sort")
 }
 
 func TestGoListCgo(t *testing.T) {

src/cmd/go/internal/list/list.go

@@ -335,6 +335,7 @@ func runList(cmd *base.Command, args []string) {
 		// Show vendor-expanded paths in listing
 		p.TestImports = p.Resolve(p.TestImports)
 		p.XTestImports = p.Resolve(p.XTestImports)
+		p.DepOnly = !cmdline[p]
 	}
 
 	if *listTest {