Put Chrome's Clang on VM slave PATH.

~/slavebin is put first on every slave's path, so that's the easiest way
to get Chrome's build of Clang there.

Here's a build that just worked with this done manually:
http://build.chromium.org/p/client.skia/builders/Test-Ubuntu13.10-GCE-NoGPU-x86_64-Release-TSAN/builds/37

You can see it using Chrome's Clang (3.6) in the "build dm" step.

BUG=skia:3026

Review URL: https://codereview.chromium.org/655243003
Sheriff dashboard / alert server

BUG=skia:3036

Review URL: https://codereview.chromium.org/608013003
Added code to fetch data from the server and display it in a Flot canvas.

Still based on the Angular.js/Bootstrap template, but separates UI/Angular code from logic as much as possible.
To be converted to Polymer.

To make the front-end easier we made some changes to the backend.

BUG=skia:

Review URL: https://codereview.chromium.org/649873004
Add Galaxy S4 slaves

BUG=skia:3032

Review URL: https://codereview.chromium.org/667163003