tools: Flesh out the gerrit package

Add more helpers for interfacing with Gerrit.

Move dawn-specific constants out to a new 'dawn' package. Keeps the
packages dawn-specific-free.

Bug: dawn:1342
Change-Id: Iaebe0b68d877340fc848d711c848d01705ddae57
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/86524
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Ben Clayton <bclayton@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>

tools/src/dawn/dawn.go

@@ -0,0 +1,19 @@
+// Copyright 2022 The Dawn Authors.
+//
+// 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.
+
+// Package dawn holds constants specific to the Dawn project
+package dawn
+
+// The Dawn gerrit URL
+const GerritURL = "https://dawn-review.googlesource.com/"