Count closures using the feedback vector cell map, specialize if count==1.

test/cctest/test-compiler.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 367 matching lines @@
   for (int i = 0; i < 3; i++) {
     LocalContext env;
     env->Global()
         ->Set(env.local(), v8_str("x"), v8::Integer::New(CcTest::isolate(), i))
         .FromJust();
     CompileRun(
         "function MakeClosure() {"
         "  return function() { return x; };"
         "}"
         "var closure0 = MakeClosure();"
+        "var closure1 = MakeClosure();"  // We only share optimized code
+                                         // if there are at least two closures.
         "%DebugPrint(closure0());"
         "%OptimizeFunctionOnNextCall(closure0);"
         "%DebugPrint(closure0());"
-        "var closure1 = MakeClosure(); closure1();"
+        "closure1();"
         "var closure2 = MakeClosure(); closure2();");
     Handle<JSFunction> fun1 = Handle<JSFunction>::cast(
         v8::Utils::OpenHandle(*v8::Local<v8::Function>::Cast(
             env->Global()
                 ->Get(env.local(), v8_str("closure1"))
                 .ToLocalChecked())));
     Handle<JSFunction> fun2 = Handle<JSFunction>::cast(
         v8::Utils::OpenHandle(*v8::Local<v8::Function>::Cast(
             env->Global()
                 ->Get(env.local(), v8_str("closure2"))
@@ skipping 264 matching lines @@
   CompileRun("foo()");
   CHECK_EQ(2, foo->feedback_vector()->invocation_count());
   CompileRun("bar()");
   CHECK_EQ(2, foo->feedback_vector()->invocation_count());
   CompileRun("foo(); foo()");
   CHECK_EQ(4, foo->feedback_vector()->invocation_count());
   CompileRun("%BaselineFunctionOnNextCall(foo);");
   CompileRun("foo();");
   CHECK_EQ(5, foo->feedback_vector()->invocation_count());
 }