Remove the debugger_ field from Isolate in a PRODUCT build

runtime/vm/runtime_entry.cc

Index: runtime/vm/runtime_entry.cc
diff --git a/runtime/vm/runtime_entry.cc b/runtime/vm/runtime_entry.cc
index 53db05703ff88e3a23ed3f24bf9e00ff94ec3f64..3dd92e0bc9d9e9557ca534d9f768f698c17825d0 100644
--- a/runtime/vm/runtime_entry.cc
+++ b/runtime/vm/runtime_entry.cc
@@ -770,7 +770,12 @@ static void CheckResultError(const Object& result) {
   }
 }
 
-#if !defined(TARGET_ARCH_DBC)
+#if defined(PRODUCT)
+DEFINE_RUNTIME_ENTRY(BreakpointRuntimeHandler, 0) {
+  UNREACHABLE();
+  return;
+}
+#elif !defined(TARGET_ARCH_DBC)
 // Gets called from debug stub when code reaches a breakpoint
 // set on a runtime stub call.
 DEFINE_RUNTIME_ENTRY(BreakpointRuntimeHandler, 0) {
@@ -808,6 +813,10 @@ DEFINE_RUNTIME_ENTRY(BreakpointRuntimeHandler, 0) {
 #endif  // !defined(TARGET_ARCH_DBC)
 
 DEFINE_RUNTIME_ENTRY(SingleStepHandler, 0) {
+#if defined(PRODUCT)
+  UNREACHABLE();
+  return;
+#else
   if (!FLAG_support_debugger) {
     UNREACHABLE();
     return;
@@ -818,6 +827,7 @@ DEFINE_RUNTIME_ENTRY(SingleStepHandler, 0) {
     Exceptions::PropagateError(error);
     UNREACHABLE();
   }
+#endif
 }
 
 // An instance call of the form o.f(...) could not be resolved.  Check if
@@ -1691,6 +1701,7 @@ DEFINE_RUNTIME_ENTRY(StackOverflow, 0) {
     }
 #endif
   }
+#if !defined(PRODUCT)
   if (FLAG_support_debugger && do_stacktrace) {
     String& var_name = String::Handle();
     Instance& var_value = Instance::Handle();
@@ -1723,6 +1734,7 @@ DEFINE_RUNTIME_ENTRY(StackOverflow, 0) {
     }
     FLAG_stacktrace_every = saved_stacktrace_every;
   }
+#endif  // !defined(PRODUCT)
 
   const Error& error = Error::Handle(thread->HandleInterrupts());
   if (!error.IsNull()) {