[Debugger] Add a ReturnValueScope to correctly handle return values in nested debug breaks.

src/debug/debug.h

 // 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.
 
 #ifndef V8_DEBUG_DEBUG_H_
 #define V8_DEBUG_DEBUG_H_
 
 #include "src/allocation.h"
 #include "src/assembler.h"
 #include "src/base/atomicops.h"
@@ skipping 375 matching lines @@
   inline bool is_loaded() const { return !debug_context_.is_null(); }
   inline bool in_debug_scope() const {
     return !!base::NoBarrier_Load(&thread_local_.current_debug_scope_);
   }
   void set_break_points_active(bool v) { break_points_active_ = v; }
   bool break_points_active() const { return break_points_active_; }
 
   StackFrame::Id break_frame_id() { return thread_local_.break_frame_id_; }
   int break_id() { return thread_local_.break_id_; }
 
+  Handle<Object> return_value_handle() {
+    return handle(thread_local_.return_value_, isolate_);
+  }
   Object* return_value() { return thread_local_.return_value_; }
   void set_return_value(Object* value) { thread_local_.return_value_ = value; }
 
   // Support for embedding into generated code.
   Address is_active_address() {
     return reinterpret_cast<Address>(&is_active_);
   }
 
   Address hook_on_function_call_address() {
     return reinterpret_cast<Address>(&hook_on_function_call_);
@@ skipping 279 matching lines @@
   // Get the active context from before entering the debugger.
   inline Handle<Context> GetContext() { return save_.context(); }
 
  private:
   Isolate* isolate() { return debug_->isolate_; }
 
   Debug* debug_;
   DebugScope* prev_;               // Previous scope if entered recursively.
   StackFrame::Id break_frame_id_;  // Previous break frame id.
   int break_id_;                   // Previous break id.
-  Handle<Object> return_value_;    // Previous result.
   bool failed_;                    // Did the debug context fail to load?
   SaveContext save_;               // Saves previous context.
   PostponeInterruptsScope no_termination_exceptons_;
 };
 
+// This scope is used to handle return values in nested debug break points.
+// When there are nested debug breaks, we use this to restore the return
+// value to the previous state. This is not merged with DebugScope because
+// return_value_ will not be cleared when we use DebugScope.
+class ReturnValueScope {
+ public:
+  explicit ReturnValueScope(Debug* debug);
+  ~ReturnValueScope();
+
+ private:
+  Debug* debug_;
+  Handle<Object> return_value_;  // Previous result.
+};
 
 // Stack allocated class for disabling break.
 class DisableBreak BASE_EMBEDDED {
  public:
   explicit DisableBreak(Debug* debug)
       : debug_(debug), previous_break_disabled_(debug->break_disabled_) {
     debug_->break_disabled_ = true;
   }
   ~DisableBreak() {
     debug_->break_disabled_ = previous_break_disabled_;
@@ skipping 62 matching lines @@
                                   Handle<Code> code);
   static bool DebugBreakSlotIsPatched(Address pc);
   static void ClearDebugBreakSlot(Isolate* isolate, Address pc);
 };
 
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_DEBUG_DEBUG_H_