Update travis with mono_repo magic

Author: kevmoo

.travis.yml

@@ -0,0 +1,26 @@
+# Created with https://github.com/dart-lang/mono_repo
+language: dart
+
+dart:
+  - dev
+  - stable
+
+env:
+  - PKG=json_serializable TASK=dartanalyzer
+  - PKG=json_serializable TASK=dartfmt
+  - PKG=json_serializable TASK=test
+
+matrix:
+  excludes:
+    - dart: stable
+      env: PKG=json_serializable TASK=dartfmt
+
+script: ./tool/travis.sh
+
+# Only building master means that we don't run two builds for each pull request.
+branches:
+  only: [master]
+
+cache:
+ directories:
+   - $HOME/.pub-cache

tool/travis.sh

@@ -0,0 +1,34 @@
+#!/bin/bash
+# Created with https://github.com/dart-lang/mono_repo
+
+# Fast fail the script on failures.
+set -e
+
+if [ -z "$PKG" ]; then
+  echo -e "PKG environment variable must be set!"
+  exit 1
+elif [ -z "$TASK" ]; then
+  echo -e "TASK environment variable must be set!"
+  exit 1
+fi
+
+pushd $PKG
+pub upgrade
+
+case $TASK in
+dartanalyzer) echo
+  echo -e "TASK: dartanalyzer"
+  dartanalyzer .
+  ;;
+dartfmt) echo
+  echo -e "TASK: dartfmt"
+  dartfmt -n --set-exit-if-changed .
+  ;;
+test) echo
+  echo -e "TASK: test"
+  pub run test --run-skipped
+  ;;
+*) echo -e "Not expecting TASK '${TASK}'. Error!"
+  exit 1
+  ;;
+esac