Add a TouchEventStreamValidator

content/common/input/gesture_event_stream_validator.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_COMMON_INPUT_GESTURE_EVENT_STREAM_VALIDATOR
 #define CONTENT_COMMON_INPUT_GESTURE_EVENT_STREAM_VALIDATOR
 
+#include <string>
+
 #include "base/basictypes.h"
 
 namespace blink {
 class WebGestureEvent;
 }
 
 namespace content {
 
-// In debug mode, logs an error and exits if the stream of WebGestureEvents
-// passed to Validate is invalid.
+// Utility class for validating a stream of WebGestureEvents.
 class GestureEventStreamValidator {
  public:
   GestureEventStreamValidator();
   ~GestureEventStreamValidator();
-  // Returns true iff |event| is valid for the current stream.
-  bool Validate(const blink::WebGestureEvent& event,
-                const char** error_message);
+
+  // If |event| is valid for the current stream, returns true.
+  // Otherwise, returns false with a corresponding error message.
+  bool Validate(const blink::WebGestureEvent& event, std::string* error_msg);
 
  private:
   bool scrolling_;
   bool pinching_;
   bool waiting_for_tap_end_;
 
   DISALLOW_COPY_AND_ASSIGN(GestureEventStreamValidator);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_COMMON_INPUT_GESTURE_EVENT_STREAM_VALIDATOR