Add a message size check to channel-associated interfaces

Adds a message size check to the case where
ChannelAssociatedGroupController must post a task to the IO thread
before sending a message. This will allow us to extract useful stack
information from such message size violations.

Bug: 840388
Change-Id: I6861252dcc3451d4551c84e7e389566e8c62dced
Reviewed-on: https://chromium-review.googlesource.com/1059587Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Commit-Queue: Ken Rockot <rockot@chromium.org>
Cr-Commit-Position: refs/heads/master@{#558849}

ipc/ipc_mojo_bootstrap.cc

@@ -28,6 +28,7 @@
 #include "base/trace_event/memory_allocator_dump.h"
 #include "base/trace_event/memory_dump_manager.h"
 #include "base/trace_event/memory_dump_provider.h"
+#include "ipc/ipc_channel.h"
 #include "mojo/public/cpp/bindings/associated_group.h"
 #include "mojo/public/cpp/bindings/associated_group_controller.h"
 #include "mojo/public/cpp/bindings/connector.h"
@@ -649,6 +650,10 @@ class ChannelAssociatedGroupController
       }
       return connector_->Accept(message);
     } else {
+      // Do a message size check here so we don't lose valuable stack
+      // information to the task scheduler.
+      CHECK_LE(message->data_num_bytes(), Channel::kMaximumMessageSize);
+
       // We always post tasks to the master endpoint thread when called from
       // other threads in order to simulate IPC::ChannelProxy::Send behavior.
       task_runner_->PostTask(