Intentionally crash DM to make sure all bots are up-to-date.

NOTREECHECKS=true
NOTRY=true
BUG=skia:

Review URL: https://codereview.chromium.org/1274693002 .

dm/DM.cpp

@@ -846,6 +846,7 @@ int dm_main() {
 
 #if !defined(SK_BUILD_FOR_IOS)
 int main(int argc, char** argv) {
+    SkASSERT(false);
     SkCommandLineFlags::Parse(argc, argv);
     return dm_main();
 }