Update travis for osx.

Author: pcj

.travis.yml

@@ -1,13 +1,33 @@
+# trusty beta image has jdk8, gcc4.8.4
 dist: trusty
 sudo: required
-language: node_js
+# xcode8 has jdk8
+osx_image: xcode8
+# Not technically required but suppresses 'Ruby' in Job status message.
+language: java
+
+os:
+  - linux
+  - osx
 
 env:
-  - V=0.3.2rc3 URL=https://storage.googleapis.com/bazel/0.3.2/rc3/bazel-0.3.2rc3-installer-linux-x86_64.sh FLAGS=''
-  - V=0.3.2rc2 URL=https://storage.googleapis.com/bazel/0.3.2/rc2/bazel-0.3.2rc2-installer-linux-x86_64.sh FLAGS=''
-  - V=0.3.1 URL=https://github.com/bazelbuild/bazel/releases/download/0.3.1/bazel-0.3.1-installer-linux-x86_64.sh FLAGS=''
+  - V=HEAD
+  - V=0.3.2
+  - V=0.3.1
 
 before_install:
+  - OS=linux
+  - ARCH=x86_64
+  - if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then OS=darwin; fi
+  - GH_BASE="https://github.com/bazelbuild/bazel/releases/download/$V"
+  - GH_ARTIFACT="bazel-$V-installer-$OS-$ARCH.sh"
+  - CI_BASE="http://ci.bazel.io/job/Bazel/JAVA_VERSION=1.8,PLATFORM_NAME=$OS-$ARCH/lastSuccessfulBuild/artifact/output/ci"
+  - CI_ARTIFACT="bazel--installer.sh"
+  - URL="$GH_BASE/$GH_ARTIFACT"
+  - if [[ "$V" == "HEAD" && "$OS" == "linux" ]]; then CI_ARTIFACT="`wget -qO- $CI_BASE | grep -oP 'bazel-.*?-installer.sh' | uniq`"; fi
+  - if [[ "$V" == "HEAD" && "$OS" == "osx" ]];   then CI_ARTIFACT="`wget -qO- $CI_BASE | pcregrep -o 'bazel-.*?-installer.sh' | uniq`"; fi
+  - if [[ "$V" == "HEAD" ]]; then URL="$CI_BASE/$CI_ARTIFACT"; fi
+  - echo $URL
   - wget -O install.sh $URL
   - chmod +x install.sh
   - ./install.sh --user