arc-bridge: Enable ARC with a command-line flag

We have permission to remove the build time flag in favor of a runtime
flag for enabling ARC Bridge Service, conditional on committing to a
more stable and appropriate IPC mechanism for the bridge.

BUG=559654
TEST=components_unittests

Review URL: https://codereview.chromium.org/1466143002

Cr-Original-Commit-Position: refs/heads/master@{#361484}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 89b91de77ee7fa5ac5103ff1b9355c8230abcca5

common.gypi

@@ -1563,9 +1563,6 @@
     'libjpeg_ijg_gyp_path': '<(DEPTH)/third_party/libjpeg/libjpeg.gyp',
     'libjpeg_turbo_gyp_path': '<(DEPTH)/third_party/libjpeg_turbo/libjpeg.gyp',
 
-    # ARC instance disabled by default.
-    'enable_arc%': 0,
-
     'conditions': [
       ['buildtype=="Official"', {
         # Continue to embed build meta data in Official builds, basically the
@@ -3106,9 +3103,6 @@
         # TODO: Enable on Windows too, http://crbug.com/404525
         'variables': { 'clang_warning_flags': ['-Wexit-time-destructors']},
       }],
-      ['<(enable_arc)==1', {
-        'defines': ['ENABLE_ARC=1'],
-      }],
       ['chromium_code==0', {
         'variables': {
           'clang_warning_flags': [

config/BUILD.gn

@@ -279,9 +279,6 @@ config("feature_flags") {
   if (!fieldtrial_testing_like_official_build && !is_chrome_branded) {
     defines += [ "FIELDTRIAL_TESTING_ENABLED" ]
   }
-  if (enable_arc) {
-    defines += [ "ENABLE_ARC=1" ]
-  }
 }
 
 # Debug/release ----------------------------------------------------------------

config/features.gni

@@ -202,6 +202,3 @@ enable_pre_sync_backup = is_win || is_mac || (is_linux && !is_chromeos)
 enable_webvr = is_android
 
 use_gio = is_desktop_linux && !is_headless
-
-# Chrome OS: whether to use ARC instances. Disabled by default.
-enable_arc = false