Fixing issue 1639, debugger stops stepping outside evaluate.

src/runtime.cc

Index: src/runtime.cc
diff --git a/src/runtime.cc b/src/runtime.cc
index b1010d3a6ae15b33d9ead4289220f4b17ca6a5e8..54395ca5115ffc8ce66cd71d196e5dbd38a1e196 100644
--- a/src/runtime.cc
+++ b/src/runtime.cc
@@ -11968,6 +11968,8 @@ RUNTIME_FUNCTION(MaybeObject*, Runtime_DebugEvaluateGlobal) {
   Handle<Object> result =
     Execution::Call(compiled_function, receiver, 0, NULL,
                     &has_pending_exception);
+  // Clear the oneshot breakpoints so that the debugger does not step further.
+  isolate->debug()->ClearStepping();
   if (has_pending_exception) return Failure::Exception();
   return *result;
 }