[debugger] correctly update test expectation for ThreadedDebugging.

It has been broken by
https://crrev.com/089edbfa97eab324bc463829ea03c167fdc6d45c

R=machenbach@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/1522883002

Cr-Commit-Position: refs/heads/master@{#32831}

test/cctest/test-debug.cc

@@ -5413,7 +5413,7 @@ static void ThreadedMessageHandler(const v8::Debug::Message& message) {
   if (IsBreakEventMessage(print_buffer)) {
     // Check that we are inside the while loop.
     int source_line = GetSourceLineFromBreakEventMessage(print_buffer);
-    CHECK(8 <= source_line && source_line <= 13);
+    CHECK(4 <= source_line && source_line <= 10);
     threaded_debugging_barriers.barrier_2.Wait();
   }
 }