Replaced DCHECK with CHECK to detect invalid socket usage.

Issue like 121085 or 320427 could be caused by writing request on busy sockets.

BUG=121085

Review URL: https://codereview.chromium.org/603783002

Cr-Commit-Position: refs/heads/master@{#297195}

net/socket/socket_libevent.cc

@@ -230,7 +230,7 @@ int SocketLibevent::Read(IOBuffer* buf,
   DCHECK(thread_checker_.CalledOnValidThread());
   DCHECK_NE(kInvalidSocket, socket_fd_);
   DCHECK(!waiting_connect_);
-  DCHECK(read_callback_.is_null());
+  CHECK(read_callback_.is_null());
   // Synchronous operation not supported
   DCHECK(!callback.is_null());
   DCHECK_LT(0, buf_len);
@@ -258,7 +258,7 @@ int SocketLibevent::Write(IOBuffer* buf,
   DCHECK(thread_checker_.CalledOnValidThread());
   DCHECK_NE(kInvalidSocket, socket_fd_);
   DCHECK(!waiting_connect_);
-  DCHECK(write_callback_.is_null());
+  CHECK(write_callback_.is_null());
   // Synchronous operation not supported
   DCHECK(!callback.is_null());
   DCHECK_LT(0, buf_len);

net/socket/tcp_socket_win.cc

@@ -492,7 +492,7 @@ int TCPSocketWin::Read(IOBuffer* buf,
   DCHECK(CalledOnValidThread());
   DCHECK_NE(socket_, INVALID_SOCKET);
   DCHECK(!waiting_read_);
-  DCHECK(read_callback_.is_null());
+  CHECK(read_callback_.is_null());
   DCHECK(!core_->read_iobuffer_);
 
   return DoRead(buf, buf_len, callback);
@@ -504,7 +504,7 @@ int TCPSocketWin::Write(IOBuffer* buf,
   DCHECK(CalledOnValidThread());
   DCHECK_NE(socket_, INVALID_SOCKET);
   DCHECK(!waiting_write_);
-  DCHECK(write_callback_.is_null());
+  CHECK(write_callback_.is_null());
   DCHECK_GT(buf_len, 0);
   DCHECK(!core_->write_iobuffer_);