More precise break points and stepping when debugging...

src/debug.h

Index: src/debug.h
===================================================================
--- src/debug.h	(revision 4816)
+++ src/debug.h	(working copy)
@@ -146,6 +146,11 @@
   void SetDebugBreakAtReturn();
   void ClearDebugBreakAtReturn();
 
+  bool IsDebugBreakSlot();
+  bool IsDebugBreakAtSlot();
+  void SetDebugBreakAtSlot();
+  void ClearDebugBreakAtSlot();
+
   DISALLOW_COPY_AND_ASSIGN(BreakLocationIterator);
 };
 
@@ -323,6 +328,7 @@
   enum AddressId {
     k_after_break_target_address,
     k_debug_break_return_address,
+    k_debug_break_slot_address,
     k_register_address
   };
 
@@ -342,6 +348,12 @@
     return &debug_break_return_;
   }
 
+  // Access to the debug break in debug break slot code.
+  static Code* debug_break_slot() { return debug_break_slot_; }
+  static Code** debug_break_slot_address() {
+    return &debug_break_slot_;
+  }
+
   static const int kEstimatedNofDebugInfoEntries = 16;
   static const int kEstimatedNofBreakPointsInFunction = 16;
 
@@ -370,6 +382,7 @@
   static void AfterGarbageCollection();
 
   // Code generator routines.
+  static void GenerateSlot(MacroAssembler* masm);
   static void GenerateLoadICDebugBreak(MacroAssembler* masm);
   static void GenerateStoreICDebugBreak(MacroAssembler* masm);
   static void GenerateKeyedLoadICDebugBreak(MacroAssembler* masm);
@@ -377,6 +390,7 @@
   static void GenerateConstructCallDebugBreak(MacroAssembler* masm);
   static void GenerateReturnDebugBreak(MacroAssembler* masm);
   static void GenerateStubNoRegistersDebugBreak(MacroAssembler* masm);
+  static void GenerateSlotDebugBreak(MacroAssembler* masm);
   static void GeneratePlainReturnLiveEdit(MacroAssembler* masm);
   static void GenerateFrameDropperLiveEdit(MacroAssembler* masm);
 
@@ -472,6 +486,9 @@
   // Code to call for handling debug break on return.
   static Code* debug_break_return_;
 
+  // Code to call for handling debug break in debug break slots.
+  static Code* debug_break_slot_;
+
   DISALLOW_COPY_AND_ASSIGN(Debug);
 };
 
@@ -895,6 +912,8 @@
         return reinterpret_cast<Address>(Debug::after_break_target_address());
       case Debug::k_debug_break_return_address:
         return reinterpret_cast<Address>(Debug::debug_break_return_address());
+      case Debug::k_debug_break_slot_address:
+        return reinterpret_cast<Address>(Debug::debug_break_slot_address());
       case Debug::k_register_address:
         return reinterpret_cast<Address>(Debug::register_address(reg_));
       default: