[interpreter] Ensure --debug-code works with snapshots.

src/interpreter/interpreter.cc

Index: src/interpreter/interpreter.cc
diff --git a/src/interpreter/interpreter.cc b/src/interpreter/interpreter.cc
index 1ac342d62b1a4186d5f5643e803d27101abb5a91..4fb2daf4a67af447bdf5c1c36b45aa64106bd2cb 100644
--- a/src/interpreter/interpreter.cc
+++ b/src/interpreter/interpreter.cc
@@ -53,7 +53,7 @@ Interpreter::Interpreter(Isolate* isolate) : isolate_(isolate) {
 }
 
 void Interpreter::Initialize() {
-  if (IsDispatchTableInitialized()) return;
+  if (!ShouldInitializeDispatchTable()) return;
   Zone zone(isolate_->allocator(), ZONE_NAME);
   HandleScope scope(isolate_);
 
@@ -103,6 +103,9 @@ void Interpreter::Initialize() {
       dispatch_table_[index] = dispatch_table_[illegal_index];
     }
   }
+
+  // Initialization should have been successful.
+  DCHECK(IsDispatchTableInitialized());
 }
 
 Code* Interpreter::GetBytecodeHandler(Bytecode bytecode,
@@ -213,13 +216,18 @@ CompilationJob* Interpreter::NewCompilationJob(CompilationInfo* info) {
 }
 
 bool Interpreter::IsDispatchTableInitialized() {
+  return dispatch_table_[0] != nullptr;
+}
+
+bool Interpreter::ShouldInitializeDispatchTable() {
   if (FLAG_trace_ignition || FLAG_trace_ignition_codegen ||
-      FLAG_trace_ignition_dispatches) {
+      FLAG_trace_ignition_dispatches || FLAG_debug_code) {
     // Regenerate table to add bytecode tracing operations, print the assembly
-    // code generated by TurboFan or instrument handlers with dispatch counters.
-    return false;
+    // code generated by TurboFan, instrument handlers with dispatch counters,
+    // or insert debugging code into the bytecode handlers.
+    return true;
   }
-  return dispatch_table_[0] != nullptr;
+  return !IsDispatchTableInitialized();
 }
 
 void Interpreter::TraceCodegen(Handle<Code> code) {