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

src/runtime/runtime-debug.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/v8.h"
 
 #include "src/accessors.h"
 #include "src/arguments.h"
 #include "src/compiler.h"
 #include "src/debug.h"
 #include "src/deoptimizer.h"
 #include "src/isolate-inl.h"
 #include "src/parser.h"
 #include "src/runtime/runtime.h"
 #include "src/runtime/runtime-utils.h"
 
 namespace v8 {
 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();
 }
 
 
 // Helper functions for wrapping and unwrapping stack frame ids.
 static Smi* WrapFrameId(StackFrame::Id id) {
   DCHECK(IsAligned(OffsetFrom(id), static_cast<intptr_t>(4)));
   return Smi::FromInt(id >> 2);
 }
@@ skipping 2754 matching lines @@
   return Smi::FromInt(isolate->debug()->is_active());
 }
 
 
 RUNTIME_FUNCTION(Runtime_DebugBreakInOptimizedCode) {
   UNIMPLEMENTED();
   return NULL;
 }
 }
 }  // namespace v8::internal