Always initialize the debugger eagerly.

src/x64/debug-x64.cc

Index: src/x64/debug-x64.cc
diff --git a/src/x64/debug-x64.cc b/src/x64/debug-x64.cc
index dfe5ba1eead8bb32107a9edf88d493abeb0858e1..6e0e05fda8959adee566bfabc84499465a4befb9 100644
--- a/src/x64/debug-x64.cc
+++ b/src/x64/debug-x64.cc
@@ -25,7 +25,7 @@ bool BreakLocationIterator::IsDebugBreakAtReturn()  {
 void BreakLocationIterator::SetDebugBreakAtReturn()  {
   ASSERT(Assembler::kJSReturnSequenceLength >= Assembler::kCallSequenceLength);
   rinfo()->PatchCodeWithCall(
-      debug_info_->GetIsolate()->debug()->debug_break_return()->entry(),
+      debug_info_->GetIsolate()->builtins()->Return_DebugBreak()->entry(),
       Assembler::kJSReturnSequenceLength - Assembler::kCallSequenceLength);
 }
 
@@ -55,7 +55,7 @@ bool BreakLocationIterator::IsDebugBreakAtSlot() {
 void BreakLocationIterator::SetDebugBreakAtSlot() {
   ASSERT(IsDebugBreakSlot());
   rinfo()->PatchCodeWithCall(
-      debug_info_->GetIsolate()->debug()->debug_break_slot()->entry(),
+      debug_info_->GetIsolate()->builtins()->Slot_DebugBreak()->entry(),
       Assembler::kDebugBreakSlotLength - Assembler::kCallSequenceLength);
 }