[debug] mark more unused debug API as deprecated.

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/arguments.h"
 #include "src/assembler.h"
@@ skipping 286 matching lines @@
 // debug_info which is a FixedArray. Each entry in this list is of class
 // DebugInfo.
 class Debug {
  public:
   // Debug event triggers.
   void OnDebugBreak(Handle<Object> break_points_hit);
 
   void OnThrow(Handle<Object> exception);
   void OnPromiseReject(Handle<Object> promise, Handle<Object> value);
   void OnCompileError(Handle<Script> script);
-  void OnBeforeCompile(Handle<Script> script);
   void OnAfterCompile(Handle<Script> script);
   void OnAsyncTaskEvent(Handle<String> type, Handle<Object> id,
                         Handle<String> name);
 
   // API facing.
   void SetEventListener(Handle<Object> callback, Handle<Object> data);
   void SetMessageHandler(v8::Debug::MessageHandler handler);
   MUST_USE_RESULT MaybeHandle<Object> Call(Handle<Object> fun,
                                            Handle<Object> data);
   Handle<Context> GetDebugContext();
@@ skipping 382 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_