Support for precise stepping in functions compiled before debugging was started (step 1)

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 53ba981c85b2f794dae8c0187be0a8aae3270964..aea55a932affa90b32905e2449b7dfd8bfe3cc9a 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -3685,6 +3685,11 @@ class Code: public HeapObject {
   inline bool has_deoptimization_support();
   inline void set_has_deoptimization_support(bool value);
 
+  // [has_debug_break_slots]: For FUNCTION kind, tells if it has
+  // been compiled with debug break slots.
+  inline bool has_debug_break_slots();
+  inline void set_has_debug_break_slots(bool value);
+
   // [allow_osr_at_loop_nesting_level]: For FUNCTION kind, tells for
   // how long the function has been marked for OSR and therefore which
   // level of loop nesting we are willing to do on-stack replacement
@@ -3875,11 +3880,16 @@ class Code: public HeapObject {
   static const int kBinaryOpTypeOffset = kStubMajorKeyOffset + 1;
   static const int kCompareStateOffset = kStubMajorKeyOffset + 1;
   static const int kToBooleanTypeOffset = kStubMajorKeyOffset + 1;
-  static const int kHasDeoptimizationSupportOffset = kOptimizableOffset + 1;
+
+  static const int kFullCodeFlags = kOptimizableOffset + 1;
+  static const int kFullCodeFlagsHasDeoptimizationSupportShift = 0;
+  static const int kFullCodeFlagsHasDebugBreakSlotsShift    = 1;
+  static const int kFullCodeFlagsHasDeoptimizationSupportMask = 0x01;
+  static const int kFullCodeFlagsHasDebugBreakSlotsMask    = 0x02;
 
   static const int kBinaryOpReturnTypeOffset = kBinaryOpTypeOffset + 1;
-  static const int kAllowOSRAtLoopNestingLevelOffset =
-      kHasDeoptimizationSupportOffset + 1;
+
+  static const int kAllowOSRAtLoopNestingLevelOffset = kFullCodeFlags + 1;
 
   static const int kSafepointTableOffsetOffset = kStackSlotsOffset + kIntSize;
   static const int kStackCheckTableOffsetOffset = kStackSlotsOffset + kIntSize;
@@ -3887,6 +3897,7 @@ class Code: public HeapObject {
   // Flags layout.
   static const int kFlagsICStateShift        = 0;
   static const int kFlagsICInLoopShift       = 3;
+
   static const int kFlagsTypeShift           = 4;
   static const int kFlagsKindShift           = 8;
   static const int kFlagsICHolderShift       = 12;