Add kokoro job for publishing javadoc to GCS

.kokoro/release/publish_javadoc.cfg

@@ -0,0 +1,16 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+env_vars: {
+  key: "TRAMPOLINE_BUILD_FILE"
+  value: "github/google-auth-library-java/.kokoro/release/publish_javadoc.sh"
+}
+
+env_vars: {
+  key: "LINK_LATEST"
+  value: false
+}
+
+env_vars: {
+  key: "BUCKET"
+  value: "gcloud-javadoc-testing"
+}

.kokoro/release/publish_javadoc.sh

@@ -0,0 +1,65 @@
+#!/bin/bash
+# Copyright 2018, Google Inc. All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met:
+#
+#    * Redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer.
+#    * Redistributions in binary form must reproduce the above
+# copyright notice, this list of conditions and the following disclaimer
+# in the documentation and/or other materials provided with the
+# distribution.
+#
+#    * Neither the name of Google Inc. nor the names of its
+# contributors may be used to endorse or promote products derived from
+# this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+set -e
+
+if [[ -z "${BUCKET}" ]]; then
+    echo "Must set BUCKET environment variable"
+    exit 1
+fi
+
+pushd $(dirname "$0")/../../
+
+# Pull the library version from project properties
+VERSION=$(mvn org.apache.maven.plugins:maven-help-plugin:2.1.1:evaluate -Dexpression=project.version | grep -Ev '(^\[|\w+:)')
+
+case "${VERSION}" in
+    *-SNAPSHOT)
+        echo "Cannot publish javadoc for -SNAPSHOT versions"
+        exit 1
+        ;;
+    "")
+        echo "Could not obtain version number from maven-help-plugin."
+        exit 1
+        ;;
+esac
+
+# Generate the javadoc from scratch
+mvn clean install javadoc:aggregate -DskipTests=true -B
+
+# Sync the current version to gCS
+gsutil -m rsync -d target/site gs://${BUCKET}/java/google-auth-library-java/${VERSION}
+
+if [[ "${LINK_LATEST}" == "true" ]]; then
+    # Sync the current content to latest
+    gsutil -m rsync gs://${BUCKET}/java/google-auth-library-java/${VERSION} gs://${BUCKET}/java/google-auth-library-java/latest
+fi
+
+popd