More precise break points and stepping when debugging...

src/assembler.h

Index: src/assembler.h
===================================================================
--- src/assembler.h	(revision 4816)
+++ src/assembler.h	(working copy)
@@ -118,9 +118,9 @@
   enum Mode {
     // Please note the order is important (see IsCodeTarget, IsGCRelocMode).
     CONSTRUCT_CALL,  // code target that is a call to a JavaScript constructor.
-    CODE_TARGET_CONTEXT,  // code target used for contextual loads.
-    DEBUG_BREAK,
-    CODE_TARGET,         // code target which is not any of the above.
+    CODE_TARGET_CONTEXT,  // Code target used for contextual loads.
+    DEBUG_BREAK,  // Code target for the debugger statement.
+    CODE_TARGET,  // Code target which is not any of the above.
     EMBEDDED_OBJECT,
 
     // Everything after runtime_entry (inclusive) is not GC'ed.
@@ -129,6 +129,7 @@
     COMMENT,
     POSITION,  // See comment for kNoPosition above.
     STATEMENT_POSITION,  // See comment for kNoPosition above.
+    DEBUG_BREAK_SLOT,  // Additional code inserted for debug break slot.
     EXTERNAL_REFERENCE,  // The address of an external C++ function.
     INTERNAL_REFERENCE,  // An address inside the same function.
 
@@ -174,6 +175,9 @@
   static inline bool IsInternalReference(Mode mode) {
     return mode == INTERNAL_REFERENCE;
   }
+  static inline bool IsDebugBreakSlot(Mode mode) {
+    return mode == DEBUG_BREAK_SLOT;
+  }
   static inline int ModeMask(Mode mode) { return 1 << mode; }
 
   // Accessors
@@ -243,6 +247,10 @@
   // with a call to the debugger.
   INLINE(bool IsPatchedReturnSequence());
 
+  // Check whether this debug break slot has been patched with a call to the
+  // debugger.
+  INLINE(bool IsPatchedDebugBreakSlotSequence());
+
 #ifdef ENABLE_DISASSEMBLER
   // Printing
   static const char* RelocModeName(Mode rmode);