LongTaskTiming: add idl, Experiment flag, PerformanceEntry and basic implementation

third_party/WebKit/Source/core/timing/PerformanceEntry.h

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  * Copyright (C) 2012 Intel Inc. 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.
@@ skipping 40 matching lines @@
 public:
     virtual ~PerformanceEntry();
 
     enum EntryType {
         Invalid = 0,
         Composite = 1 << 1,
         Mark = 1 << 2,
         Measure = 1 << 3,
         Render = 1 << 4,
         Resource = 1 << 5,
+        LongTask = 1 << 6,
     };
 
     String name() const;
     String entryType() const;
     double startTime() const;
     double duration() const;
 
     ScriptValue toJSONForBinding(ScriptState*) const;
 
     PerformanceEntryType entryTypeEnum() const { return m_entryTypeEnum; }
@@ skipping 21 matching lines @@
     const String m_name;
     const String m_entryType;
     const double m_startTime;
     const double m_duration;
     const PerformanceEntryType m_entryTypeEnum;
 };
 
 } // namespace blink
 
 #endif // PerformanceEntry_h