Add UMA to track the number of live URLRequests.

net/url_request/url_request_context.h

Index: net/url_request/url_request_context.h
diff --git a/net/url_request/url_request_context.h b/net/url_request/url_request_context.h
index d34c2fdb3bb59c3396b32c99f8e990ce219f6b6f..206b01059971c7fb906723599c16146afe158b2b 100644
--- a/net/url_request/url_request_context.h
+++ b/net/url_request/url_request_context.h
@@ -221,10 +221,14 @@ class NET_EXPORT URLRequestContext
 
   // Gets the URLRequest objects that hold a reference to this
   // URLRequestContext.
-  std::set<const URLRequest*>* url_requests() const {
-    return url_requests_.get();
+  const std::set<const URLRequest*>& url_requests() const {
+    return url_requests_;
   }
 
+  void InsertURLRequest(const URLRequest* request) const;
+
+  void RemoveURLRequest(const URLRequest* request) const;
+
   // CHECKs that no URLRequests using this context remain. Subclasses should
   // additionally call AssertNoURLRequests() within their own destructor,
   // prior to implicit destruction of subclass-owned state.
@@ -312,7 +316,7 @@ class NET_EXPORT URLRequestContext
   // be added to CopyFrom.
   // ---------------------------------------------------------------------------
 
-  std::unique_ptr<std::set<const URLRequest*>> url_requests_;
+  mutable std::set<const URLRequest*> url_requests_;
 
   // Enables Brotli Content-Encoding support.
   bool enable_brotli_;
@@ -325,6 +329,10 @@ class NET_EXPORT URLRequestContext
   // to be unique.
   const char* name_;
 
+  // The largest number of outstanding URLRequests that have been created by
+  // |this| and are not yet destroyed. This doesn't need to be in CopyFrom.
+  mutable size_t largest_outstanding_requests_count_seen_;
+
   DISALLOW_COPY_AND_ASSIGN(URLRequestContext);
 };