Merged r12019 into 3.10 branch.

src/debug.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 971 matching lines @@
     // and keep step count queued up in the meantime.
     if (step_action == StepNext && frame->fp() < thread_local_.last_fp_) {
       // Count frames until target frame
       int count = 0;
       JavaScriptFrameIterator it(isolate_);
       while (!it.done() && it.frame()->fp() != thread_local_.last_fp_) {
         count++;
         it.Advance();
       }
 
-      // If we found original frame
-      if (it.frame()->fp() == thread_local_.last_fp_) {
-        if (step_count > 1) {
-          // Save old count and action to continue stepping after
-          // StepOut
-          thread_local_.queued_step_count_ = step_count - 1;
-        }
+      // Check that we indeed found the frame we are looking for.
+      CHECK(!it.done() && (it.frame()->fp() == thread_local_.last_fp_));
+      if (step_count > 1) {
+        // Save old count and action to continue stepping after
+        // StepOut
+        thread_local_.queued_step_count_ = step_count - 1;
+      }
 
-        // Set up for StepOut to reach target frame
-        step_action = StepOut;
-        step_count = count;
-      }
+      // Set up for StepOut to reach target frame
+      step_action = StepOut;
+      step_count = count;
     }
 
     // Clear all current stepping setup.
     ClearStepping();
 
     // Set up for the remaining steps.
     PrepareStep(step_action, step_count);
   }
 
   if (thread_local_.frame_drop_mode_ == FRAMES_UNTOUCHED) {
@@ skipping 2568 matching lines @@
     {
       Locker locker;
       Isolate::Current()->debugger()->CallMessageDispatchHandler();
     }
   }
 }
 
 #endif  // ENABLE_DEBUGGER_SUPPORT
 
 } }  // namespace v8::internal