chore(travis): add npm/install-dependencies.sh step in preparation for caching

.travis.yml

@@ -28,12 +28,22 @@ before_install:
 - ./scripts/ci/install_dart.sh ${DART_CHANNEL} ${ARCH}
 - sh -e /etc/init.d/xvfb start
 - if [[ -e SKIP_TRAVIS_TESTS ]]; then { cat SKIP_TRAVIS_TESTS ; exit 0; } fi
+
+install:
+  # Check the size of caches
+  - du -sh ./node_modules || true
+  # Install npm dependecies and ensure that npm cache is not stale
+  - tools/npm/install-dependencies.sh
+
 before_script:
 - mkdir -p $LOGS_DIR
+
 script:
 - ./scripts/ci/build_and_test.sh ${MODE}
+
 after_script:
 - ./scripts/ci/print-logs.sh
+
 notifications:
   webhooks:
     urls:

tools/npm/install-dependencies.sh

@@ -0,0 +1,16 @@
+#!/bin/bash
+
+set -e
+
+SHRINKWRAP_FILE=npm-shrinkwrap.json
+SHRINKWRAP_CACHED_FILE=node_modules/npm-shrinkwrap.cached.json
+
+if diff -q $SHRINKWRAP_FILE $SHRINKWRAP_CACHED_FILE; then
+  echo 'No shrinkwrap changes detected. npm install will be skipped...';
+else
+  echo 'Blowing away node_modules and reinstalling npm dependencies...'
+  rm -rf node_modules
+  npm install
+  cp $SHRINKWRAP_FILE $SHRINKWRAP_CACHED_FILE
+  echo 'npm install successful!'
+fi