[Bindings] Make maplike<> and setlike<> imply a readonly size attribute.

third_party/WebKit/public/platform/WebRTCStats.h

 // Copyright 2016 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 WebRTCStats_h
 #define WebRTCStats_h
 
 #include "WebCommon.h"
 #include "WebString.h"
 #include "WebVector.h"
@@ skipping 30 matching lines @@
   virtual ~WebRTCStatsReport();
   // Creates a new report object that is a handle to the same underlying stats
   // report (the stats are not copied). The new report's iterator is reset,
   // useful when needing multiple iterators.
   virtual std::unique_ptr<WebRTCStatsReport> CopyHandle() const = 0;
 
   // Gets stats object by |id|, or null if no stats with that |id| exists.
   virtual std::unique_ptr<WebRTCStats> GetStats(WebString id) const = 0;
   // The next stats object, or null if the end has been reached.
   virtual std::unique_ptr<WebRTCStats> Next() = 0;
+  // The number of stats objects.
+  virtual size_t Size() const = 0;
 };
 
 class BLINK_PLATFORM_EXPORT WebRTCStats {
  public:
   virtual ~WebRTCStats();
 
   virtual WebString Id() const = 0;
   virtual WebString GetType() const = 0;
   virtual double Timestamp() const = 0;
 
@@ skipping 31 matching lines @@
 class BLINK_PLATFORM_EXPORT WebRTCStatsReportCallback {
  public:
   virtual ~WebRTCStatsReportCallback();
 
   virtual void OnStatsDelivered(std::unique_ptr<WebRTCStatsReport>) = 0;
 };
 
 }  // namespace blink
 
 #endif  // WebRTCStats_h