Fix device_forwarder build with FORTIFY_SOURCE.

tools/android/forwarder2/forwarder.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "tools/android/forwarder2/forwarder.h"
 
 #include "base/basictypes.h"
 #include "base/logging.h"
 #include "base/posix/eintr_wrapper.h"
 #include "tools/android/forwarder2/socket.h"
@@ skipping 118 matching lines @@
         break;
 
       case STATE_CLOSED:
         return;
     }
     *max_fd = std::max(*max_fd, fd);
   }
 
   // Call this after a select() call to operate over the buffer.
   void ProcessSelect(const fd_set& read_fds, const fd_set& write_fds) {
-    int fd, ret;
+    int fd;
+    int ret;
+    // With FORTIFY_SOURCE, FD_ISSET is implemented as a function that takes a
+    // non-const fd_set*. Make a copy of the passed arguments so we can safely
+    // take a reference.
+    fd_set read_fds_copy = read_fds;
+    fd_set write_fds_copy = write_fds;
     switch (state_) {
       case STATE_READING:
         fd = socket_from_->fd();
         if (fd < 0) {
           state_ = STATE_CLOSED;  // T02
           return;
         }
-        if (!FD_ISSET(fd, &read_fds))
+        if (!FD_ISSET(fd, &read_fds_copy))
           return;
 
         ret = socket_from_->NonBlockingRead(buffer_, kBufferSize);
         if (ret <= 0) {
           ForceClose();  // T02
           return;
         }
         bytes_read_ = ret;
         write_offset_ = 0;
         state_ = STATE_WRITING;  // T01
         break;
 
       case STATE_WRITING:
       case STATE_CLOSING:
         fd = socket_to_->fd();
         if (fd < 0) {
           ForceClose();  // T06 + T11
           return;
         }
-        if (!FD_ISSET(fd, &write_fds))
+        if (!FD_ISSET(fd, &write_fds_copy))
           return;
 
         ret = socket_to_->NonBlockingWrite(buffer_ + write_offset_,
                                            bytes_read_ - write_offset_);
         if (ret <= 0) {
           ForceClose();  // T06 + T11
           return;
         }
 
         write_offset_ += ret;
@@ skipping 68 matching lines @@
   return buffer1_->is_closed() && buffer2_->is_closed();
 }
 
 void Forwarder::Shutdown() {
   DCHECK(thread_checker_.CalledOnValidThread());
   buffer1_->Close();
   buffer2_->Close();
 }
 
 }  // namespace forwarder2