Use goma on headless bots

BUG=632008

Review-Url: https://codereview.chromium.org/2367723002
Cr-Commit-Position: refs/heads/master@{#421208}

build/args/bots/chromium.fyi/headless_linux_dbg.gn

 import("//build/args/headless.gn")
 is_debug = true
+use_goma = true

build/args/bots/tryserver.chromium.linux/headless_linux_dbg_trybot.gn

 import("//build/args/headless.gn")
 is_debug = true
+use_goma = true
 symbol_level = 1