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

src/debug.cc

Index: src/debug.cc
diff --git a/src/debug.cc b/src/debug.cc
index 5d26ba2b139e36fc8704678c4b2c1919b74447a8..0917fea9ac99c19e1fd6bc2b8b40f211037dedc2 100644
--- a/src/debug.cc
+++ b/src/debug.cc
@@ -390,6 +390,20 @@ void BreakLocationIterator::ClearDebugBreak() {
 }
 
 
+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);