all: add go.mod

Commands run:
	go mod init
	go mod edit -go=1.11
	go mod tidy
	go list -m all
	go test ./...

Updates golang/go#30228
Updates golang/go#27234

Change-Id: Ibf3b104bfaa037e1a94a5327b5a56983d9744e73
Reviewed-on: https://go-review.googlesource.com/c/mobile/+/167180
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

go.mod

@@ -0,0 +1,9 @@
+module golang.org/x/mobile
+
+go 1.11
+
+require (
+	golang.org/x/exp v0.0.0-20190306152737-a1d7652674e8
+	golang.org/x/image v0.0.0-20190227222117-0694c2d4d067
+	golang.org/x/sys v0.0.0-20190312061237-fead79001313 // indirect
+)

go.sum

@@ -0,0 +1,7 @@
+golang.org/x/exp v0.0.0-20190306152737-a1d7652674e8 h1:idBdZTd9UioThJp8KpM/rTSinK/ChZFBE43/WtIy8zg=
+golang.org/x/exp v0.0.0-20190306152737-a1d7652674e8/go.mod h1:CJ0aWSM057203Lf6IL+f9T1iT9GByDxfZKAQTCR3kQA=
+golang.org/x/image v0.0.0-20190227222117-0694c2d4d067 h1:KYGJGHOQy8oSi1fDlSpcZF0+juKwk/hEMv5SiwHogR0=
+golang.org/x/image v0.0.0-20190227222117-0694c2d4d067/go.mod h1:kZ7UVZpmo3dzQBMxlp+ypCbDeSB+sBbTgSJuh5dn5js=
+golang.org/x/sys v0.0.0-20190312061237-fead79001313 h1:pczuHS43Cp2ktBEEmLwScxgjWsBSzdaQiKzUyf3DTTc=
+golang.org/x/sys v0.0.0-20190312061237-fead79001313/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=