Revert "Simplify debugger state."

src/execution.cc

 // 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.
 
 #include "execution.h"
 
 #include "bootstrapper.h"
 #include "codegen.h"
 #include "deoptimizer.h"
 #include "isolate-inl.h"
@@ skipping 696 matching lines @@
                             !isolate->stack_guard()->CheckDebugBreak();
 
   isolate->stack_guard()->ClearDebugBreak();
 
   Execution::ProcessDebugMessages(isolate, debug_command_only);
 }
 
 
 void Execution::ProcessDebugMessages(Isolate* isolate,
                                      bool debug_command_only) {
+  // Assert that we are on the main thread of the isolate.
+  ASSERT(ThreadId::Current().Equals(isolate->thread_id()));
+
   isolate->stack_guard()->ClearDebugCommand();
 
   StackLimitCheck check(isolate);
   if (check.HasOverflowed()) return;
 
   HandleScope scope(isolate);
   // Enter the debugger. Just continue if we fail to enter the debugger.
   EnterDebugger debugger(isolate);
   if (debugger.FailedToEnter()) return;
 
@@ skipping 39 matching lines @@
     isolate_->optimizing_compiler_thread()->InstallOptimizedFunctions();
   }
 
   isolate_->counters()->stack_interrupts()->Increment();
   isolate_->counters()->runtime_profiler_ticks()->Increment();
   isolate_->runtime_profiler()->OptimizeNow();
   return isolate_->heap()->undefined_value();
 }
 
 } }  // namespace v8::internal