Fallback to IPv6 if IPv4 adb port not available.

chrome/test/chromedriver/net/adb_client_socket.cc

Index: chrome/test/chromedriver/net/adb_client_socket.cc
diff --git a/chrome/test/chromedriver/net/adb_client_socket.cc b/chrome/test/chromedriver/net/adb_client_socket.cc
index 9a5a672c6bc7e69fc06f35237c67cd837b01f100..05478c9f517a42842fec280733c6f3e97898ee36 100644
--- a/chrome/test/chromedriver/net/adb_client_socket.cc
+++ b/chrome/test/chromedriver/net/adb_client_socket.cc
@@ -365,8 +365,16 @@ AdbClientSocket::~AdbClientSocket() {
 }
 
 void AdbClientSocket::Connect(const net::CompletionCallback& callback) {
-  net::AddressList address_list = net::AddressList::CreateFromIPAddress(
-      net::IPAddress::IPv4Localhost(), port_);
+  // getaddrinfo for localhost could only return IPv6 address in a IPv4/IPv6
+  // dual stack environment while current adb (1.0.36) always listen on IPv4.

[samuong, 2016/09/23 10:01:15]

I'd suggest the following tweak to the wording to make it a bit clearer that adb
listens on IPv6 when running in an IPv6-only environment:

In a IPv4/IPv6 dual stack environment, getaddrinfo for localhost could only
return IPv6 address while the current adb (1.0.36) will always listen on IPv4.

+  // So just try IPv4 first, then fall back to IPv6.
+  net::IPAddressList list = {net::IPAddress::IPv4Localhost(),
+                             net::IPAddress::IPv6Localhost()};
+  net::AddressList ip_list = net::AddressList::CreateFromIPAddressList(
+      list, "localhost");
+  net::AddressList address_list = net::AddressList::CopyWithPort(
+      ip_list, port_);
+
   socket_.reset(new net::TCPClientSocket(address_list, NULL, NULL,
                                          net::NetLog::Source()));
   int result = socket_->Connect(callback);