perfetto-ui: Add release build to waterfall

Both emscripten[1] and node[2] (and by extension third party modules
we bundle or may bundle for the UI[3]) differentiate between debug and
release builds/runtimes. We probably want to use the debug version
locally and the release version when shipping so we should test both versions
on the CI. We can reuse is_debug to control NODE_ENV - but this can be done
in a follow up.

[1]: http://kripken.github.io/emscripten-site/docs/optimizing/Optimizing-Code.html#how-to-optimize-code
[2]: https://expressjs.com/en/advanced/best-practice-performance.html#set-node_env-to-production
[3]: https://github.com/reduxjs/redux/blob/4a215fb74167675485df7d6d2fb1197a184cc461/src/index.js#L16

Change-Id: I631d50a5a61e7f969ae00f56a09a4cd250a07ca9
diff --git a/.travis.yml b/.travis.yml
index c3c153a..7425aba 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -101,6 +101,12 @@
       sudo: false
       compiler: clang
       env: CFG=ui-clang-x86_64-release GN_ARGS="is_debug=false is_clang=true"
+    - os: linux
+      dist: trusty
+      sudo: false
+      compiler: clang
+      env: CFG=ui-clang-x86_64-debug GN_ARGS="is_debug=true is_clang=true"
+
 
 # Cache the deps that get git-pulled to avoid hitting quota limits (b/68252114).
 # Do not cache NDK/SDK and things that come from .zip files rather than git.