[interpreter, debugger] implement bytecode break location iterator.

src/interpreter/source-position-table.cc

Index: src/interpreter/source-position-table.cc
diff --git a/src/interpreter/source-position-table.cc b/src/interpreter/source-position-table.cc
index 2a8800548bd76bd499de5a5c591e3433ed02687b..72ce7d5268cbbcf911910ad63e0840b1144fb4fd 100644
--- a/src/interpreter/source-position-table.cc
+++ b/src/interpreter/source-position-table.cc
@@ -18,7 +18,7 @@ class SourcePositionField : public BitField<int, 1, 30> {};
 void SourcePositionTableBuilder::AddStatementPosition(size_t bytecode_offset,
                                                       int source_position) {
   int offset = static_cast<int>(bytecode_offset);
-  AssertMonotonic(offset);
+  if (AlreadyHasPosition(offset)) return;
   uint32_t encoded = IsStatementField::encode(true) |
                      SourcePositionField::encode(source_position);
   entries_.push_back({offset, encoded});
@@ -27,7 +27,7 @@ void SourcePositionTableBuilder::AddStatementPosition(size_t bytecode_offset,
 void SourcePositionTableBuilder::AddExpressionPosition(size_t bytecode_offset,
                                                        int source_position) {
   int offset = static_cast<int>(bytecode_offset);
-  AssertMonotonic(offset);
+  if (AlreadyHasPosition(offset)) return;
   uint32_t encoded = IsStatementField::encode(false) |
                      SourcePositionField::encode(source_position);
   entries_.push_back({offset, encoded});