Add a Mojo EDK for Chrome that uses one OS pipe per message pipe.

ipc/mojo/async_handle_waiter.cc

Index: ipc/mojo/async_handle_waiter.cc
diff --git a/ipc/mojo/async_handle_waiter.cc b/ipc/mojo/async_handle_waiter.cc
index b9e68d7c4539886059b8428617eb43121eb19b4d..652764edc6c763e6d17fdd5746955edc513394e0 100644
--- a/ipc/mojo/async_handle_waiter.cc
+++ b/ipc/mojo/async_handle_waiter.cc
@@ -86,6 +86,11 @@ class AsyncHandleWaiter::Context
   }
 
   void DidProcessIOEvent() override {
+    // This object could have been constructed in another's class's
+    // DidProcessIOEvent.
+    if (io_loop_level_== 0)
+      return;
+
     DCHECK_GE(io_loop_level_, 1);
 
     // Leaving a nested loop.