Version 4.6.13.1 (cherry-pick)

src/debug.cc

Index: src/debug.cc
diff --git a/src/debug.cc b/src/debug.cc
index 1d90c2999a2bd0efb19080b1fac1ccca6beffaa7..6d033a7416e191a80bba50cdab215f61025a506e 100644
--- a/src/debug.cc
+++ b/src/debug.cc
@@ -2735,8 +2735,19 @@ void Debug::HandleDebugBreak() {
   bool debug_command_only = isolate_->stack_guard()->CheckDebugCommand() &&
                             !isolate_->stack_guard()->CheckDebugBreak();
 
+  bool is_debugger_statement = !isolate_->stack_guard()->CheckDebugCommand() &&
+                               !isolate_->stack_guard()->CheckDebugBreak();
+
   isolate_->stack_guard()->ClearDebugBreak();
 
+  if (is_debugger_statement) {
+    // If we have been called via 'debugger' Javascript statement,
+    // we might not be prepared for breakpoints.
+    // TODO(dslomov,yangguo): CheckDebugBreak may race with RequestDebugBreak.
+    // Revisit this to clean-up.
+    HandleScope handle_scope(isolate_);
+    PrepareForBreakPoints();
+  }
   ProcessDebugMessages(debug_command_only);
 }