[debugger] fix step-next for tail calls.

src/debug/debug.h

Index: src/debug/debug.h
diff --git a/src/debug/debug.h b/src/debug/debug.h
index 3e59adea1d0637c7e6a464cbc8be892a097ac0a4..35aa8db049624e89de125cc57fd2ccc3ffd4c9f5 100644
--- a/src/debug/debug.h
+++ b/src/debug/debug.h
@@ -81,6 +81,9 @@ class BreakLocation {
 
   inline bool IsReturn() const { return type_ == DEBUG_BREAK_SLOT_AT_RETURN; }
   inline bool IsCall() const { return type_ == DEBUG_BREAK_SLOT_AT_CALL; }
+  inline bool IsTailCall() const {
+    return type_ == DEBUG_BREAK_SLOT_AT_TAIL_CALL;
+  }
   inline bool IsDebugBreakSlot() const { return type_ >= DEBUG_BREAK_SLOT; }
   inline bool IsDebuggerStatement() const {
     return type_ == DEBUGGER_STATEMENT;
@@ -113,7 +116,8 @@ class BreakLocation {
     DEBUGGER_STATEMENT,
     DEBUG_BREAK_SLOT,
     DEBUG_BREAK_SLOT_AT_CALL,
-    DEBUG_BREAK_SLOT_AT_RETURN
+    DEBUG_BREAK_SLOT_AT_RETURN,
+    DEBUG_BREAK_SLOT_AT_TAIL_CALL,
   };
 
   BreakLocation(Handle<DebugInfo> debug_info, DebugBreakType type,
@@ -140,6 +144,8 @@ class BreakLocation {
     explicit Iterator(Handle<DebugInfo> debug_info);
     int ReturnPosition();
 
+    Isolate* isolate() { return debug_info_->GetIsolate(); }
+
     Handle<DebugInfo> debug_info_;
     int break_index_;
     int position_;
@@ -166,7 +172,7 @@ class BreakLocation {
     }
 
    private:
-    static int GetModeMask(BreakLocatorType type);
+    int GetModeMask(BreakLocatorType type);
     RelocInfo::Mode rmode() { return reloc_iterator_.rinfo()->rmode(); }
     RelocInfo* rinfo() { return reloc_iterator_.rinfo(); }