Re-commit "win: Set is_clang=true by default" over the weekend.

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 02af1d3ef17fa6a9d4af3bbf6e04d35a31fa6b3c..753909556a0a387534a1b0f307dde3d3cd2364de 100644
--- a/tools/mb/mb_config.pyl
+++ b/tools/mb/mb_config.pyl
@@ -1042,7 +1042,10 @@
     ],
 
     'clang_debug_bot_minimal_symbols_x86': [
-      'clang', 'debug_bot', 'minimal_symbols', 'x86',
+      # Now that the default win bots use clang, use a "clang" bot to make sure
+      # things stay compilable with msvc. TODO(thakis): Having a "clang" bot
+      # check that is very confusing, so rename the bot to "msvc".
+      'no_clang', 'debug_bot', 'minimal_symbols', 'x86',
     ],
 
     'clang_release_bot_minimal_symbols_x86': [
@@ -1050,15 +1053,24 @@
     ],
 
     'clang_minimal_symbols_shared_release_bot_x86_dcheck': [
-      'clang', 'minimal_symbols', 'shared_release_bot', 'x86', 'dcheck_always_on',
+      # Now that the default win bots use clang, use a "clang" bot to make sure
+      # things stay compilable with msvc. TODO(thakis): Having a "clang" bot
+      # check that is very confusing, so rename the bot to "msvc".
+      'no_clang', 'minimal_symbols', 'shared_release_bot', 'x86', 'dcheck_always_on',
     ],
 
     'clang_official_release_bot_minimal_symbols': [
-      'clang', 'official', 'release_bot', 'minimal_symbols',
+      # Now that the default win bots use clang, use a "clang" bot to make sure
+      # things stay compilable with msvc. TODO(thakis): Having a "clang" bot
+      # check that is very confusing, so rename the bot to "msvc".
+      'no_clang', 'official', 'release_bot', 'minimal_symbols',
     ],
 
     'clang_official_release_bot_minimal_symbols_x86': [
-      'clang', 'official', 'release_bot', 'minimal_symbols', 'x86',
+      # Now that the default win bots use clang, use a "clang" bot to make sure
+      # things stay compilable with msvc. TODO(thakis): Having a "clang" bot
+      # check that is very confusing, so rename the bot to "msvc".
+      'no_clang', 'official', 'release_bot', 'minimal_symbols', 'x86',
     ],
 
     'clang_official_optimize_release_bot_minimal_symbols_x86': [
@@ -1074,7 +1086,10 @@
     ],
 
     'clang_shared_release_bot_dcheck': [
-      'clang', 'shared_release_bot', 'dcheck_always_on',
+      # Now that the default win bots use clang, use a "clang" bot to make sure
+      # things stay compilable with msvc. TODO(thakis): Having a "clang" bot
+      # check that is very confusing, so rename the bot to "msvc".
+      'no_clang', 'shared_release_bot', 'dcheck_always_on',
     ],
 
     'clang_tot_asan_lsan_static_release': [
@@ -1497,7 +1512,10 @@
     ],
 
     'win_clang_debug_bot': [
-      'clang', 'debug_bot', 'minimal_symbols',
+      # Now that the default win bots use clang, use a "clang" bot to make sure
+      # things stay compilable with msvc. TODO(thakis): Having a "clang" bot
+      # check that is very confusing, so rename the bot to "msvc".
+      'no_clang', 'debug_bot', 'minimal_symbols',
     ],
 
     'windows_analyze': [
@@ -1587,11 +1605,11 @@
     },
 
     'chrome_pgo_phase_1': {
-      'gn_args': 'chrome_pgo_phase=1',
+      'gn_args': 'chrome_pgo_phase=1 is_clang=false',
     },
 
     'chrome_pgo_phase_2': {
-      'gn_args': 'chrome_pgo_phase=2',
+      'gn_args': 'chrome_pgo_phase=2 is_clang=false',
     },
 
     'chrome_with_codecs': {
@@ -1867,7 +1885,8 @@
     },
 
     'syzyasan': {
-      'gn_args': 'is_syzyasan=true',
+      # TODO(thakis): Figure out SyzyASan + clang story.
+      'gn_args': 'is_syzyasan=true is_clang=false',
     },
 
     'thin_lto': {