Add tests for Headless Linux bot

tools/mb/mb_config.pyl

Index: tools/mb/mb_config.pyl
diff --git a/tools/mb/mb_config.pyl b/tools/mb/mb_config.pyl
index 6581a3ccedcb393d8e6161bfe2a8dbc134eed321..09184c8eeaf106d3aa97409ada02174e6ec42e68 100644
--- a/tools/mb/mb_config.pyl
+++ b/tools/mb/mb_config.pyl
@@ -202,6 +202,7 @@
       'Chromium_iOS_Device_(ninja)': 'ios_gyp',
       'Chromium_iOS_Simulator_(dbg)': 'ios_gyp',
       'CrWinClang64(dbg)': 'win_clang_debug_bot',
+      'Headless Linux (dbg)': 'gn_headless_debug_bot',
       'Libfuzzer Upload Linux ASan': 'gn_release_libfuzzer_asan',
       'Libfuzzer Upload Linux MSan': 'gn_release_libfuzzer_msan',
       'Libfuzzer Upload Linux UBSan': 'gn_release_libfuzzer_ubsan',
@@ -1117,6 +1118,10 @@
       'gyp', 'release_trybot', 'x64',
     ],
 
+    'gn_headless_debug_bot': [
+      'gn', 'headless', 'debug_bot',
+    ],
+
     'gn_release_libfuzzer_asan': [
       'gn', 'release', 'libfuzzer', 'asan', 'proprietary_codecs', 'pdf_xfa',
       'disable_nacl',
@@ -1127,7 +1132,7 @@
       'disable_nacl',
     ],
     'gn_release_libfuzzer_ubsan': [
-      'gn', 'release', 'libfuzzer', 'ubsan_security', 'proprietary_codecs', 
+      'gn', 'release', 'libfuzzer', 'ubsan_security', 'proprietary_codecs',
       'pdf_xfa', 'disable_nacl',
     ],
 
@@ -1147,7 +1152,7 @@
     ],
 
     'gyp_windows_analyze': [
-      'gyp', 'no_symbols', 'disable_precompiled_headers', 
+      'gyp', 'no_symbols', 'disable_precompiled_headers',
       'shared', 'x86', 'win_analyze',
     ],
 
@@ -1625,6 +1630,15 @@
 
     'gyp': {'type': 'gyp'},
 
+    # TODO(skyostil): Consider replacing the 'is_headless' flag with a
+    # //build/args config template.
+    'headless': {
+      'gn_args': 'is_headless=true',
+
+      # It's an error to combine this with the gyp mixin.
+      'gyp_defines': 'target_arch=unknown',
+    },
+
     'internal_gles2_conform_tests': {
       'gn_args': 'internal_gles2_conform_tests=true',
       'gyp_defines': 'internal_gles2_conform_tests=1',