Provide list of step-in source positions in JS Debug API

src/debug.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 372 matching lines @@
     // Restore the code in the break slot.
     ClearDebugBreakAtSlot();
   } else {
     // Patch the IC call.
     ClearDebugBreakAtIC();
   }
   ASSERT(!IsDebugBreak());
 }
 
 
+bool BreakLocationIterator::IsStepInLocation(Isolate* isolate) {
+  if (RelocInfo::IsConstructCall(rmode())) {
+    return true;
+  } else if (RelocInfo::IsCodeTarget(rmode())) {
+    HandleScope scope(debug_info_->GetIsolate());
+    Address target = rinfo()->target_address();
+    Handle<Code> target_code(Code::GetCodeFromTargetAddress(target));
+    return target_code->is_call_stub() || target_code->is_keyed_call_stub();
+  } else {
+    return false;
+  }
+}
+
+
 void BreakLocationIterator::PrepareStepIn(Isolate* isolate) {
   HandleScope scope(isolate);
 
   // Step in can only be prepared if currently positioned on an IC call,
   // construct call or CallFunction stub call.
   Address target = rinfo()->target_address();
   Handle<Code> target_code(Code::GetCodeFromTargetAddress(target));
   if (target_code->is_call_stub() || target_code->is_keyed_call_stub()) {
     // Step in through IC call is handled by the runtime system. Therefore make
     // sure that the any current IC is cleared and the runtime system is
@@ skipping 3396 matching lines @@
     {
       Locker locker(reinterpret_cast<v8::Isolate*>(isolate_));
       isolate_->debugger()->CallMessageDispatchHandler();
     }
   }
 }
 
 #endif  // ENABLE_DEBUGGER_SUPPORT
 
 } }  // namespace v8::internal