Fix data race in IPC::ChannelProxy

Fixes a missing lock acquisition from the listener thread when
accessing |channel_|.

Also removes the TSAN suppression for this bug.

BUG=628481
TBR=glider@chromium.org for suppression removal

Review-Url: https://codereview.chromium.org/2158893002
Cr-Commit-Position: refs/heads/master@{#406033}

build/sanitizers/tsan_suppressions.cc

@@ -267,9 +267,6 @@ char kTSanDefaultSuppressions[] =
 // http://crbug.com/582274
 "race:usrsctp_close\n"
 
-// http://crbug.com/628481
-"race:IPC::SyncChannel::SyncContext::OnChannelClose\n"
-
 // End of suppressions.
 ;  // Please keep this semicolon.
 

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()));
+      }
     }
   }