[debugger] Ensure at least one breakable position per function.

src/interpreter/source-position-table.cc

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/interpreter/source-position-table.h"
 
 #include "src/objects-inl.h"
 #include "src/objects.h"
 
 namespace v8 {
@@ skipping 133 matching lines @@
   SubtractFromEntry(tmp, previous_);
   EncodeEntry(bytes_, tmp);
   previous_ = entry;
 
 #ifdef ENABLE_SLOW_DCHECKS
   raw_entries_.push_back(entry);
 #endif
 }
 
 Handle<ByteArray> SourcePositionTableBuilder::ToSourcePositionTable() {
+  if (bytes_.empty()) return isolate_->factory()->empty_byte_array();
+
   Handle<ByteArray> table = isolate_->factory()->NewByteArray(
       static_cast<int>(bytes_.size()), TENURED);
-  if (bytes_.empty()) return table;
 
   MemCopy(table->GetDataStartAddress(), &*bytes_.begin(), bytes_.size());
 
 #ifdef ENABLE_SLOW_DCHECKS
   // Brute force testing: Record all positions and decode
   // the entire table to verify they are identical.
   auto raw = raw_entries_.begin();
   for (SourcePositionTableIterator encoded(*table); !encoded.done();
        encoded.Advance(), raw++) {
     DCHECK(raw != raw_entries_.end());
@@ skipping 20 matching lines @@
   } else {
     PositionTableEntry tmp;
     DecodeEntry(table_, &index_, &tmp);
     AddAndSetEntry(current_, tmp);
   }
 }
 
 }  // namespace interpreter
 }  // namespace internal
 }  // namespace v8