Merge the classes Debug and Debugger.

src/isolate.h

Index: src/isolate.h
diff --git a/src/isolate.h b/src/isolate.h
index ca2c23ea74d70f4eb697286dcc77c09e65b9567b..7ecf6469634d0383dc00b14d2e6f8dc86d310576 100644
--- a/src/isolate.h
+++ b/src/isolate.h
@@ -930,7 +930,6 @@ class Isolate {
     return &interp_canonicalize_mapping_;
   }
 
-  Debugger* debugger() {  return debugger_; }
   Debug* debug() { return debug_; }
 
   inline bool DebuggerHasBreakPoints();
@@ -1260,7 +1259,6 @@ class Isolate {
   JSObject::SpillInformation js_spill_information_;
 #endif
 
-  Debugger* debugger_;
   Debug* debug_;
   CpuProfiler* cpu_profiler_;
   HeapProfiler* heap_profiler_;