Don't crash the renderer if the plugin crashes.

ppapi/proxy/proxy_channel.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 "ppapi/proxy/proxy_channel.h"
 
 #include "ipc/ipc_platform_file.h"
 #include "ipc/ipc_test_sink.h"
 
 namespace ppapi {
@@ skipping 32 matching lines @@
 #if defined(OS_POSIX) && !defined(OS_NACL)
 int ProxyChannel::TakeRendererFD() {
   DCHECK(channel());
   return channel()->TakeClientFileDescriptor();
 }
 #endif
 
 IPC::PlatformFileForTransit ProxyChannel::ShareHandleWithRemote(
       base::PlatformFile handle,
       bool should_close_source) {
+  // Channel could be closed if the plugin crashes.
+  if (!channel_.get())
+    return IPC::InvalidPlatformFileForTransit();
   return delegate_->ShareHandleWithRemote(handle, *channel_,
                                           should_close_source);
 }
 
 bool ProxyChannel::Send(IPC::Message* msg) {
   if (test_sink_)
     return test_sink_->Send(msg);
   if (channel_.get())
     return channel_->Send(msg);
 
   // Remote side crashed, drop this message.
   delete msg;
   return false;
 }
 
 }  // namespace proxy
 }  // namespace ppapi