Use http protocol for periodic connectivity check

Https is quite heavy for periodic connectivity check. Change to http
version to reduce the server load after initial https check passsed.

Bug: b/135769650
Test: Verified the check change to http one after last check succeed.
Change-Id: I73d0c9ffaa6a22d0319d6782ed17ee1152045894
Signed-off-by: Edward Wang <wangedward@google.com>
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1677263Reviewed-by: Sergey Volk <servolk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#672661}

chromecast/net/connectivity_checker_impl.cc

@@ -47,6 +47,10 @@ const unsigned int kRequestTimeoutInSeconds = 3;
 const char kDefaultConnectivityCheckUrl[] =
     "https://connectivitycheck.gstatic.com/generate_204";
 
+// Http url for connectivity checking.
+const char kHttpConnectivityCheckUrl[] =
+    "http://connectivitycheck.gstatic.com/generate_204";
+
 // Delay notification of network change events to smooth out rapid flipping.
 // Histogram "Cast.Network.Down.Duration.In.Seconds" shows 40% of network
 // downtime is less than 3 seconds.
@@ -119,6 +123,17 @@ void ConnectivityCheckerImpl::SetConnected(bool connected) {
     base::AutoLock auto_lock(connected_lock_);
     connected_ = connected;
   }
+
+  base::CommandLine* command_line = base::CommandLine::ForCurrentProcess();
+  base::CommandLine::StringType check_url_str =
+      command_line->GetSwitchValueNative(switches::kConnectivityCheckUrl);
+  if (check_url_str.empty())
+  {
+    connectivity_check_url_.reset(new GURL(
+      connected ? kHttpConnectivityCheckUrl : kDefaultConnectivityCheckUrl));
+    LOG(INFO) << "Change check url=" << *connectivity_check_url_;
+  }
+
   Notify(connected);
   LOG(INFO) << "Global connection is: " << (connected ? "Up" : "Down");
 }