[debugger] correctly find source position of implicit return statement.

src/objects.cc

 // Copyright 2013 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/objects.h"
 
 #include <cmath>
 #include <iomanip>
 #include <sstream>
 
@@ skipping 11336 matching lines @@
   const int src_len = src.length();
   UnicodeCache* cache = isolate->unicode_cache();
   for (int i = 0; i < src_len - 1; i++) {
     SourceChar current = src[i];
     SourceChar next = src[i + 1];
     if (cache->IsLineTerminatorSequence(current, next)) line_ends->Add(i);
   }
 
   if (src_len > 0 && cache->IsLineTerminatorSequence(src[src_len - 1], 0)) {
     line_ends->Add(src_len - 1);
-  } else if (include_ending_line) {
-    // Even if the last line misses a line end, it is counted.
+  }
+  if (include_ending_line) {
+    // Include one character beyond the end of script. The rewriter uses that
+    // position for the implicit return statement.
     line_ends->Add(src_len);
   }
 }
 
 
 Handle<FixedArray> String::CalculateLineEnds(Handle<String> src,
                                              bool include_ending_line) {
   src = Flatten(src);
   // Rough estimate of line count based on a roughly estimated average
   // length of (unpacked) code.
@@ skipping 7914 matching lines @@
   if (cell->value() != *new_value) {
     cell->set_value(*new_value);
     Isolate* isolate = cell->GetIsolate();
     cell->dependent_code()->DeoptimizeDependentCodeGroup(
         isolate, DependentCode::kPropertyCellChangedGroup);
   }
 }
 
 }  // namespace internal
 }  // namespace v8