Remove special debug ExternalReferences.

src/assembler.h

Index: src/assembler.h
diff --git a/src/assembler.h b/src/assembler.h
index 6d67fc1cb8e3eedeb863ed0905a748b58cf55cb9..2d9bde6fe383ddefa430e4b4333c0403c4538907 100644
--- a/src/assembler.h
+++ b/src/assembler.h
@@ -794,8 +794,6 @@ class ExternalReference BASE_EMBEDDED {
 
   ExternalReference(const IC_Utility& ic_utility, Isolate* isolate);
 
-  ExternalReference(const Debug_Address& debug_address, Isolate* isolate);
-
   explicit ExternalReference(StatsCounter* counter);
 
   ExternalReference(Isolate::AddressId id, Isolate* isolate);
@@ -915,6 +913,10 @@ class ExternalReference BASE_EMBEDDED {
 
   static ExternalReference cpu_features();
 
+  static ExternalReference debug_after_break_target_address(Isolate* isolate);
+  static ExternalReference debug_restarter_frame_function_pointer_address(
+      Isolate* isolate);
+
   static ExternalReference is_profiling_address(Isolate* isolate);
   static ExternalReference invoke_function_callback(Isolate* isolate);
   static ExternalReference invoke_accessor_getter_callback(Isolate* isolate);