[debugger] flood function for stepping before calling it.

src/debug/debug.cc

 // Copyright 2012 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/debug/debug.h"
 
 #include "src/api.h"
 #include "src/arguments.h"
 #include "src/bootstrapper.h"
 #include "src/code-stubs.h"
@@ skipping 713 matching lines @@
   }
   // Remove all debug info.
   while (debug_info_list_ != NULL) {
     RemoveDebugInfoAndClearFromShared(debug_info_list_->debug_info());
   }
 }
 
 
 void Debug::FloodWithOneShot(Handle<JSFunction> function,
                              BreakLocatorType type) {
+  if (!function->shared()->IsSubjectToDebugging()) {
+    // Builtin functions are not subject to stepping, but need to be
+    // deoptimized, because optimized code does not check for debug
+    // step in at call sites.
+    Deoptimizer::DeoptimizeFunction(*function);
+    return;
+  }
   // Make sure the function is compiled and has set up the debug info.
   Handle<SharedFunctionInfo> shared(function->shared());
   if (!EnsureDebugInfo(shared, function)) {
     // Return if we failed to retrieve the debug info.
     return;
   }
 
   // Flood the function with break points.
   Handle<DebugInfo> debug_info(shared->GetDebugInfo());
   for (BreakLocation::Iterator it(debug_info, type); !it.Done(); it.Next()) {
@@ skipping 1858 matching lines @@
 }
 
 
 void LockingCommandMessageQueue::Clear() {
   base::LockGuard<base::Mutex> lock_guard(&mutex_);
   queue_.Clear();
 }
 
 }  // namespace internal
 }  // namespace v8