Fix FunctionTester constructor from given parameter count.

test/cctest/compiler/function-tester.h

 // Copyright 2014 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_CCTEST_COMPILER_FUNCTION_TESTER_H_
 #define V8_CCTEST_COMPILER_FUNCTION_TESTER_H_
 
 #include "src/ast/ast-numbering.h"
 #include "src/ast/scopes.h"
 #include "src/compiler.h"
@@ skipping 188 matching lines @@
     CHECK(!code.is_null());
     info.dependencies()->Commit(code);
     info.context()->native_context()->AddOptimizedCode(*code);
     function->ReplaceCode(*code);
     return function;
   }
 
   std::string BuildFunction(int param_count) {
     std::string function_string = "(function(";
     if (param_count > 0) {
-      char next = 'a';
-      function_string += next;
-      while (param_count-- > 0) {
+      function_string += 'a';
+      for (int i = 1; i < param_count; i++) {
         function_string += ',';
-        function_string += ++next;
+        function_string += static_cast<char>('a' + i);
       }
     }
     function_string += "){})";
     return function_string;
   }
 
   std::string BuildFunctionFromDescriptor(
       const CallInterfaceDescriptor& descriptor) {
     return BuildFunction(descriptor.GetParameterCount());
   }
@@ skipping 14 matching lines @@
     CHECK(!code.is_null());
     function->ReplaceCode(*code);
     return function;
   }
 };
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_CCTEST_COMPILER_FUNCTION_TESTER_H_