Implement SOCKS5 authentication.

[riastradh-brave]

• Work around Chromium's new in-line constructor size limits.

• Get base::StringPiece forward declaration in url_auth_util.h.

• Use `#if !defined(BRAVE_CHROMIUM_BUILD)', not #if 0.

• Override and include, rather than patch, net_log_event_type_list.h.

• Override and include host_port_pair.cc to reduce BUILD.gn diffs.

• Override and include url_util.cc rather than add url_auth_util.cc.

• Override and include socks5_client_socket.cc.

• Don't patch HostPortPair(host, port) constructor.

  Instead, use a different constructor in proxy_server.cc.

  This adds another patch to our maintenance burden, but it avoids
  changing the semantics of (and adding parsing overhead to) the
  constructor that is used in a bazillion places all over Chromium.

This is a replacement for #290, in which during squashing or something I lost two files (socks5_client_socket.cc/h) that were critical to the whole thing, and for #302, which was behind a Chromium update or something, and for #311, which had a larger set of patches than necessary.

fix brave/brave-browser#666

Submitter Checklist:

• Submitted a ticket for my issue if one did not already exist.
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests).
• Ran git rebase -i to squash commits (if needed).
• Tagged reviewers and labelled the pull request as needed.
• Request a security/privacy review as needed.

Test Plan:

On riastradh-socks5-auth-test-v3 (which only adds tests, doesn't touch anything used outside tests):

• ninja -C src/out/Debug net:net_unittests
• ./src/out/Debug/net_unittests --gtest_filter='ProxyServerTest.*:SOCKS5ClientSocketTest.*'

Reviewer Checklist:

• New files have MPL-2.0 license header.
• Request a security/privacy review as needed.
• Adequate test coverage exists to prevent regressions

[darkdh]

build pass on all platforms. However, ProxyServerTest.*:SOCKS5ClientSocketTest.* unit test only pass fro Mac and Linux
I saw these on Windows

5 tests crashed:
    SOCKS5ClientSocketTest.CompleteHandshake (../../net/socket/socks5_client_socket_unittest.cc:125)
    SOCKS5ClientSocketTest.ConnectAndDisconnectTwice (../../net/socket/socks5_client_socket_unittest.cc:196)
    SOCKS5ClientSocketTest.LargeHostNameFails (../../net/socket/socks5_client_socket_unittest.cc:232)
    SOCKS5ClientSocketTest.PartialReadWrites (../../net/socket/socks5_client_socket_unittest.cc:250)
    SOCKS5ClientSocketTest.Tag (../../net/socket/socks5_client_socket_unittest.cc:379)

Crash stacks are almost the same cause

Received fatal exception EXCEPTION_ACCESS_VIOLATION
Backtrace:
        std::char_traits<char>::assign [0x00007FFAD6EB48C8+24] (C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Tools\MSVC\14.11.25503\include\iosfwd:517)
        std::basic_string<char,std::char_traits<char>,std::allocator<char> >::assign [0x00007FFAD6EB4522+162] (C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Tools\MSVC\14.11.25503\include\xstring:2441)
        std::basic_string<char,std::char_traits<char>,std::allocator<char> >::operator= [0x00007FFAD6EB5EE0+144] (C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Tools\MSVC\14.11.25503\include\xstring:2267)
        net::HostPortPair::operator= [0x00007FFAD6ECB51E+62] (C:\brave-browser\src\net\base\host_port_pair.h:21)
        net::ProxyServer::operator= [0x00007FFAD6FAE98C+60] (C:\brave-browser\src\net\base\proxy_server.h:25)
        net::HttpResponseInfo::operator= [0x00007FFAD6FAF8CF+111] (C:\brave-browser\src\net\http\http_response_info.cc:131)
        net::ClientSocketHandle::ResetErrorState [0x00007FFAD6FF556E+78] (C:\brave-browser\src\net\socket\client_socket_handle.cc:87)
        net::ClientSocketHandle::Reset [0x00007FFAD6FF5027+39] (C:\brave-browser\src\net\socket\client_socket_handle.cc:48)
        net::ClientSocketHandle::~ClientSocketHandle [0x00007FFAD6FF4F78+24] (C:\brave-browser\src\net\socket\client_socket_handle.cc:32)
        std::default_delete<net::ClientSocketHandle>::operator() [0x00007FFAD6FFE3EC+44] (C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Tools\MSVC\14.11.25503\include\memory:1999)
        std::unique_ptr<net::ClientSocketHandle,std::default_delete<net::ClientSocketHandle> >::~unique_ptr [0x00007FFAD6FF466B+75] (C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Tools\MSVC\14.11.25503\include\memory:2204)
        net::SOCKS5ClientSocket::~SOCKS5ClientSocket [0x00007FFAD769866D+141] (C:\brave-browser\src\net\socket\socks5_client_socket.cc:52)
...

[darkdh]

the above error turns out to be causing by sccache.
I did fresh build without using sccache and it works great and no test crash and startup crash
The build result sccache gave us is missing two members we patched username_ and password_
I inspect the object instance(HostPortPair) that being assigned, it only contains host_ and port_

[darkdh]

All build pass, ProxyServerTest.*:SOCKS5ClientSocketTest.* unit tests pass and manually set --proxy-server with different credentials get different ip on https://check.torproject.org/ pass