Rework how remoting JS compilation GYP works.

There was an unfortunate bug that swallowed Java stacks.
Issues were discovered when Java stacks started surfacing:
https://codereview.chromium.org/476453002/

So change the way remoting is built. It doesn't need to be
built on all bots by default: they have undefined Java versions
and likely weren't working before (and shouldn't differ).

Instead, run when run_jscompile=1 is defined in GYP:

  export GYP_DEFINES=run_jscompile=1 && build/gyp_chromium
  # or add in ~/.gyp/includes.gypi or $SRC/../chromium.gyp_env
  # or build/gyp_chromium -Drun_jscompile=1

and on the Closure Compilation Linux FYI bot:
http://build.chromium.org/p/chromium.fyi/builders/Closure%20Compilation%20Linux

This also fixes some GYP inputs problems (if I changed compile_js.gypi or
other things in remoting/ ninja wouldn't rebuild anything).

[email protected]
BUG=none
TEST=green bots, remoting runs on Closure Compliation Linux FYI bot

Review URL: https://codereview.chromium.org/1037613002

Cr-Commit-Position: refs/heads/master@{#322193}
5 files changed