Reapply "[vm] Don't enable the profiler by default. Enable the profiler at startup with --observe, …

runtime/bin/main.cc

Index: runtime/bin/main.cc
diff --git a/runtime/bin/main.cc b/runtime/bin/main.cc
index a430f8d1f5185e299cf76eb85f6ab822e6397667..9022af0d7ae16bc4e7dc11594b144129e5b74303 100644
--- a/runtime/bin/main.cc
+++ b/runtime/bin/main.cc
@@ -456,6 +456,7 @@ static bool ProcessObserveOption(const char* option_value,
   // These options should also be documented in the help message.
   vm_options->AddArgument("--pause-isolates-on-exit");
   vm_options->AddArgument("--pause-isolates-on-unhandled-exceptions");
+  vm_options->AddArgument("--profiler");
   vm_options->AddArgument("--warn-on-pause-with-no-debugger");
   return true;
 }