[libfuzzer] separate libfuzzer ubsan configuration and ubsan build config setup.

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 6417815df8c8417116cd7791f43746c636993720..bfcf270851a8ff49271232fa862f4536b90c2bf7 100644
--- a/tools/mb/mb_config.pyl
+++ b/tools/mb/mb_config.pyl
@@ -204,6 +204,7 @@
       'CrWinClang64(dbg)': 'win_clang_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',
       'Linux ARM': 'swarming_gyp_release_bot_arm',
       'Site Isolation Linux': 'gn_release_trybot',
       'Site Isolation Win': 'gyp_release_trybot_x64',
@@ -1125,6 +1126,10 @@
     'gn_release_libfuzzer_msan': [
       'gn', 'release', 'libfuzzer', 'msan', 'proprietary_codecs', 'pdf_xfa',
     ],
+    'gn_release_libfuzzer_ubsan': [
+      'gn', 'release', 'libfuzzer', 'libfuzzer_ubsan', 'proprietary_codecs', 
+      'pdf_xfa',
+    ],
 
     'gn_release_drmemory_drfuzz_x86': [
       'gn', 'release', 'drmemory', 'drfuzz', 'x86', 'proprietary_codecs',
@@ -1626,6 +1631,7 @@
     },
 
     'libfuzzer': { 'gn_args': 'use_libfuzzer=true' },
+    'libfuzzer_ubsan': { 'gn_args': 'is_libfuzzer_ubsan=true' },
 
     'lsan': {
       'gn_args': 'is_lsan=true',