[interpreter, debugger] implement bytecode break location iterator.

src/interpreter/source-position-table.h

 // 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.
 
 #ifndef V8_INTERPRETER_SOURCE_POSITION_TABLE_H_
 #define V8_INTERPRETER_SOURCE_POSITION_TABLE_H_
 
 #include "src/assert-scope.h"
 #include "src/handles.h"
 #include "src/zone.h"
@@ skipping 17 matching lines @@
   void AddExpressionPosition(size_t bytecode_offset, int source_position);
   void RevertPosition(size_t bytecode_offset);
   Handle<FixedArray> ToFixedArray();
 
  private:
   struct Entry {
     int bytecode_offset;
     uint32_t source_position_and_type;
   };
 
-  void AssertMonotonic(int bytecode_offset) {
-    DCHECK(entries_.size() == 0 ||
-           entries_.back().bytecode_offset < bytecode_offset);
+  bool CodeOffsetHasPosition(int bytecode_offset) {
+    // Return whether bytecode offset already has a position assigned.
+    return entries_.size() > 0 &&
+           entries_.back().bytecode_offset == bytecode_offset;
   }
 
   Isolate* isolate_;
   ZoneVector<Entry> entries_;
 };
 
 class SourcePositionTableIterator {
  public:
   explicit SourcePositionTableIterator(BytecodeArray* bytecode_array);
 
@@ skipping 21 matching lines @@
   int bytecode_offset_;
   int source_position_;
   DisallowHeapAllocation no_gc;
 };
 
 }  // namespace interpreter
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_INTERPRETER_SOURCE_POSITION_TABLE_H_