Make sure debugger is ready for breakpoins when we process 'debugger' statement.

src/runtime/runtime-debug.cc

Index: src/runtime/runtime-debug.cc
diff --git a/src/runtime/runtime-debug.cc b/src/runtime/runtime-debug.cc
index e802ea6975383562edb28cf3754d23e3c733da0f..5ea98dae22c6a5d65b6619d8e5dc45edb886c77c 100644
--- a/src/runtime/runtime-debug.cc
+++ b/src/runtime/runtime-debug.cc
@@ -20,6 +20,15 @@ namespace internal {
 RUNTIME_FUNCTION(Runtime_DebugBreak) {
   SealHandleScope shs(isolate);
   DCHECK(args.length() == 0);
+  bool is_debugger_statement = !isolate->stack_guard()->CheckDebugCommand() &&
+                               !isolate->stack_guard()->CheckDebugBreak();

[yurys, 2015/03/26 19:44:48]

RequestDebugBreak can be called on another thread. It means that in the
beginning of this method CheckDebugBreak could be false while here it is already
true and is_debugger_statement will be false even though this method is called
on debugger; statement. We need a better condition for this or probably drop it
and always call PrepareForBreakPoints below.

[Yang, 2015/03/27 09:10:21]

How about we just check whether the debugger is active here, and if yes,
PrepareForBreakPoints here, and then call HandleDebugBreak? We can only end up
here via debugger statement, so we don't care about interrupts at all.

+
+  if (is_debugger_statement) {
+    // If we have been called via 'debugger' Javascript statement,
+    // we might not be prepared for breakpoints.
+    HandleScope handle_scope(isolate);
+    isolate->debug()->PrepareForBreakPoints();
+  }
   isolate->debug()->HandleDebugBreak();
   return isolate->heap()->undefined_value();
 }