Fix an off-by-one error in vmservice expression evaluation.

runtime/vm/service.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/service.h"
 
 #include "include/dart_api.h"
 #include "include/dart_native_api.h"
 #include "platform/globals.h"
 
@@ skipping 2288 matching lines @@
 
 static bool EvaluateInFrame(Thread* thread, JSONStream* js) {
   Isolate* isolate = thread->isolate();
   if (!isolate->compilation_allowed()) {
     js->PrintError(kFeatureDisabled,
                    "Cannot evaluate when running a precompiled program.");
     return true;
   }
   DebuggerStackTrace* stack = isolate->debugger()->StackTrace();
   intptr_t framePos = UIntParameter::Parse(js->LookupParam("frameIndex"));
-  if (framePos > stack->Length()) {
+  if (framePos >= stack->Length()) {
     PrintInvalidParamError(js, "frameIndex");
     return true;
   }
   ActivationFrame* frame = stack->FrameAt(framePos);
 
   Zone* zone = thread->zone();
   const char* expr = js->LookupParam("expression");
   const String& expr_str = String::Handle(zone, String::New(expr));
 
   const Object& result = Object::Handle(zone, frame->Evaluate(expr_str));
@@ skipping 1859 matching lines @@
     if (strcmp(method_name, method.name) == 0) {
       return &method;
     }
   }
   return NULL;
 }
 
 #endif  // !PRODUCT
 
 }  // namespace dart