Add accessor to read connection establishment time-point

Summary:
In furtherance of advancing connection conditioning in dependent code, the
time-point which a connection was established can be read through an
accessor.

Reviewed By: yfeldblum

Differential Revision: D8669627

fbshipit-source-id: 156924689354d7a19188f4873009e678a68be64b

folly/io/async/AsyncSocket.h

@@ -598,6 +598,14 @@ class AsyncSocket : virtual public AsyncTransportWrapper {
     return connectTimeout_;
   }
 
+  std::chrono::steady_clock::time_point getConnectStartTime() const {
+    return connectStartTime_;
+  }
+
+  std::chrono::steady_clock::time_point getConnectEndTime() const {
+    return connectEndTime_;
+  }
+
   bool getTFOAttempted() const {
     return tfoAttempted_;
   }

folly/io/async/test/AsyncSocketTest2.cpp

@@ -102,12 +102,17 @@ TEST(AsyncSocketTest, Connect) {
   EventBase evb;
   std::shared_ptr<AsyncSocket> socket = AsyncSocket::newSocket(&evb);
   ConnCallback cb;
+  const auto startedAt = std::chrono::steady_clock::now();
   socket->connect(&cb, server.getAddress(), 30);
 
   evb.loop();
+  const auto finishedAt = std::chrono::steady_clock::now();
 
   ASSERT_EQ(cb.state, STATE_SUCCEEDED);
   EXPECT_LE(0, socket->getConnectTime().count());
+  EXPECT_GE(socket->getConnectStartTime(), startedAt);
+  EXPECT_LE(socket->getConnectStartTime(), socket->getConnectEndTime());
+  EXPECT_LE(socket->getConnectEndTime(), finishedAt);
   EXPECT_EQ(socket->getConnectTimeout(), std::chrono::milliseconds(30));
 }