internal: codify tools in go.mod

Change-Id: I6c15cdf632f496114a29f0d5ef7975b4d685cf2f
Reviewed-on: https://code-review.googlesource.com/c/37130
Reviewed-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Eno Compton <enocom@google.com>
diff --git a/go.mod b/go.mod
index eec4bb3..e072e2b 100644
--- a/go.mod
+++ b/go.mod
@@ -1,11 +1,15 @@
 module google.golang.org/api
 
 require (
+	github.com/golang/protobuf v1.2.0
 	github.com/google/go-cmp v0.2.0
 	go.opencensus.io v0.18.0
+	golang.org/x/lint v0.0.0-20181026193005-c67002cb31c3
 	golang.org/x/oauth2 v0.0.0-20181203162652-d668ce993890
 	golang.org/x/sync v0.0.0-20181108010431-42b317875d0f
+	golang.org/x/tools v0.0.0-20180828015842-6cd1fcedba52
 	google.golang.org/appengine v1.3.0
 	google.golang.org/genproto v0.0.0-20181202183823-bd91e49a0898
 	google.golang.org/grpc v1.17.0
+	honnef.co/go/tools v0.0.0-20180728063816-88497007e858
 )
diff --git a/go.sum b/go.sum
index c184013..5aa63b5 100644
--- a/go.sum
+++ b/go.sum
@@ -13,6 +13,7 @@
 github.com/google/go-cmp v0.2.0 h1:+dTQ8DZQJz0Mb/HjFlkptS1FeQ4cWSnN941F8aEG4SQ=
 github.com/google/go-cmp v0.2.0/go.mod h1:oXzfMopK8JAjlY9xF4vHSVASa0yLyX7SntLO5aqRK0M=
 github.com/grpc-ecosystem/grpc-gateway v1.5.0/go.mod h1:RSKVYQBd5MCa4OVpNdGskqpgL2+G+NZTnrVHpWWfpdw=
+github.com/kisielk/gotool v1.0.0 h1:AV2c/EiW3KqPNT9ZKl07ehoAGi4C5/01Cfbblndcapg=
 github.com/kisielk/gotool v1.0.0/go.mod h1:XhKaO+MFFWcvkIS/tQcRk01m1F5IRFswLeQ+oQHNcck=
 github.com/matttproud/golang_protobuf_extensions v1.0.1/go.mod h1:D8He9yQNgCq6Z5Ld7szi9bcBfOoFv/3dc6xSMkL2PC0=
 github.com/openzipkin/zipkin-go v0.1.1/go.mod h1:NtoC/o8u3JlF1lSlyPNswIbeQH9bJTmOf0Erfk+hxe8=
@@ -23,6 +24,7 @@
 go.opencensus.io v0.18.0 h1:Mk5rgZcggtbvtAun5aJzAtjKKN/t0R3jJPlWILlv938=
 go.opencensus.io v0.18.0/go.mod h1:vKdFvxhtzZ9onBp9VKHK8z/sRpBMnKAsufL7wlDrCOA=
 golang.org/x/lint v0.0.0-20180702182130-06c8688daad7/go.mod h1:UVdnD1Gm6xHRNCYTkRU2/jEulfH38KcIWyp/GAMgvoE=
+golang.org/x/lint v0.0.0-20181026193005-c67002cb31c3 h1:x/bBzNauLQAlE3fLku/xy92Y8QwKX5HZymrMz2IiKFc=
 golang.org/x/lint v0.0.0-20181026193005-c67002cb31c3/go.mod h1:UVdnD1Gm6xHRNCYTkRU2/jEulfH38KcIWyp/GAMgvoE=
 golang.org/x/net v0.0.0-20180724234803-3673e40ba225/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
 golang.org/x/net v0.0.0-20180826012351-8a410e7b638d/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
@@ -40,6 +42,7 @@
 golang.org/x/sys v0.0.0-20180909124046-d0be0721c37e/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/text v0.3.0 h1:g61tztE5qeGQ89tm6NTjjM9VPIm088od1l6aSorWRWg=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
+golang.org/x/tools v0.0.0-20180828015842-6cd1fcedba52 h1:JG/0uqcGdTNgq7FdU+61l5Pdmb8putNZlXb65bJBROs=
 golang.org/x/tools v0.0.0-20180828015842-6cd1fcedba52/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
 google.golang.org/api v0.0.0-20180910000450-7ca32eb868bf/go.mod h1:4mhQ8q/RsB7i+udVvVy5NUi08OU8ZlA0gRVgrF7VFY0=
 google.golang.org/appengine v1.1.0/go.mod h1:EbEs0AVv82hx2wNQdGPgUI5lhzA/G0D9YwlJXL52JkM=
@@ -55,4 +58,5 @@
 google.golang.org/grpc v1.17.0/go.mod h1:6QZJwpn2B+Zp71q/5VxRsJ6NXXVCE5NRUHRo+f3cWCs=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/yaml.v2 v2.2.1/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
+honnef.co/go/tools v0.0.0-20180728063816-88497007e858 h1:wN+eVZ7U+gqdqkec6C6VXR1OFf9a5Ul9ETzeYsYv20g=
 honnef.co/go/tools v0.0.0-20180728063816-88497007e858/go.mod h1:rf3lG4BRIbNafJWhAfAdb/ePZxsR/4RtNHQocxwk9r4=
diff --git a/tools.go b/tools.go
new file mode 100644
index 0000000..ed9293a
--- /dev/null
+++ b/tools.go
@@ -0,0 +1,31 @@
+// +build tools
+
+// Copyright 2018 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// This package exists to cause `go mod` and `go get` to believe these tools
+// are dependencies, even though they are not runtime dependencies of any
+// package (these are tools used by our CI builds). This means they will appear
+// in our `go.mod` file, but will not be a part of the build. Also, since the
+// build target is something non-existent, these should not be included in any
+// binaries.
+
+package api
+
+import (
+	_ "github.com/golang/protobuf/protoc-gen-go"
+	_ "golang.org/x/lint/golint"
+	_ "golang.org/x/tools/cmd/goimports"
+	_ "honnef.co/go/tools/cmd/staticcheck"
+)