Start disabling GYP by default in runhooks in some configurations.

The grand GYP disabling is beginning ...

We want to turn of GYP by default in runhooks for configurations that
should only be using GN now.

For now we will only turnxs it off when gyp_chromium is passed the
--running-as-hook flag (which runhooks will now pass), so invoking
build/gyp_chromium will explicitly run. Also, you can set the env var
GYP_CHROMIUM_NO_ACTION=0 and it will explicitly run (setting that var
to =1 will explicitly *not* run and exit early).

This CL takes a conservative first step and turns it off for Linux
hosts that have no GYP_DEFINES set (including command line -D flags
and values pulled in from any supplemental files, chromium.gyp_env,
or ~/.gyp/include.gypi). Subsequent CLs will start broadening this.

R=thakis@chromium.org, brettw@chromium.org, scottmg@chromium.org
BUG=432967

Review URL: https://codereview.chromium.org/1883283002

Cr-Original-Commit-Position: refs/heads/master@{#387481}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 4d1f42d07135d10b5e5dc156c64cd76fde6aec79

gyp_chromium.py

@@ -320,6 +320,22 @@ def main():
   if mac_toolchain_dir:
     args.append('-Gmac_toolchain_dir=' + mac_toolchain_dir)
 
+  # TODO(crbug.com/432967) - We are eventually going to switch GYP off
+  # by default for all Chromium builds, so this list of configurations
+  # will get broader and broader.
+  running_as_hook = '--running-as-hook'
+  if (running_as_hook in args and
+      os.environ.get('GYP_CHROMIUM_NO_ACTION', None) != '0' and
+      (sys.platform.startswith('linux') and not gyp_vars_dict)):
+    print 'GYP is now disabled in this configuration by default in runhooks.\n'
+    print 'If you really want to run this, either run '
+    print '`python build/gyp_chromium.py` explicitly by hand'
+    print 'or set the environment variable GYP_CHROMIUM_NO_ACTION=0.'
+    sys.exit(0)
+
+  if running_as_hook in args:
+    args.remove(running_as_hook)
+
   if not use_analyzer:
     print 'Updating projects from gyp files...'
     sys.stdout.flush()