Fix data race in IPC::ChannelProxy

ipc/ipc_channel_proxy.cc

Index: ipc/ipc_channel_proxy.cc
diff --git a/ipc/ipc_channel_proxy.cc b/ipc/ipc_channel_proxy.cc
index 5ac51cdf961e02fd629b06404c7b7051c7235709..a4176b0a4bd339c076d7c3bedab9ae1b963ddb9d 100644
--- a/ipc/ipc_channel_proxy.cc
+++ b/ipc/ipc_channel_proxy.cc
@@ -324,12 +324,15 @@ void ChannelProxy::Context::OnDispatchConnected() {
   if (channel_connected_called_)
     return;
 
-  if (channel_) {
-    Channel::AssociatedInterfaceSupport* associated_interface_support =
-        channel_->GetAssociatedInterfaceSupport();
-    if (associated_interface_support) {
-      channel_associated_group_.reset(new mojo::AssociatedGroup(
-          *associated_interface_support->GetAssociatedGroup()));
+  {
+    base::AutoLock l(channel_lifetime_lock_);
+    if (channel_) {
+      Channel::AssociatedInterfaceSupport* associated_interface_support =
+          channel_->GetAssociatedInterfaceSupport();
+      if (associated_interface_support) {
+        channel_associated_group_.reset(new mojo::AssociatedGroup(
+            *associated_interface_support->GetAssociatedGroup()));
+      }
     }
   }