Mojo EDK: Introduce MojoQueryHandleSignalsState API

content/child/web_data_consumer_handle_impl.cc

Index: content/child/web_data_consumer_handle_impl.cc
diff --git a/content/child/web_data_consumer_handle_impl.cc b/content/child/web_data_consumer_handle_impl.cc
index b40f479861e1ba145c80e339da7f8bb6dd80d81c..5d2ac1d520b48d15e5f969f24cbf43ea86c828a7 100644
--- a/content/child/web_data_consumer_handle_impl.cc
+++ b/content/child/web_data_consumer_handle_impl.cc
@@ -62,20 +62,13 @@ Result WebDataConsumerHandleImpl::ReaderImpl::read(void* data,
     // Even if there is unread data available, mojo::ReadDataRaw() returns
     // FAILED_PRECONDITION when |size| is 0 and the producer handle was closed.
     // But in this case, WebDataConsumerHandle::Reader::read() must return Ok.
-    // So we use mojo::Wait() with 0 deadline to check whether readable or not.
-    MojoResult wait_result = mojo::Wait(
-        context_->handle().get(), MOJO_HANDLE_SIGNAL_READABLE, 0, nullptr);
-    switch (wait_result) {
-      case MOJO_RESULT_OK:
-        return Ok;
-      case MOJO_RESULT_FAILED_PRECONDITION:
-        return Done;
-      case MOJO_RESULT_DEADLINE_EXCEEDED:
-        return ShouldWait;
-      default:
-        NOTREACHED();
-        return UnexpectedError;
-    }
+    // So we query the signals state directly.
+    mojo::HandleSignalsState state = context_->handle()->QuerySignalsState();
+    if (state.readable())
+      return Ok;
+    else if (state.never_readable())

[yzshen1, 2017/03/14 18:20:44]

nit: I think the style guide says we don't need "else" in this case.

[Ken Rockot(use gerrit already), 2017/03/14 19:16:18]

Ah right, done

+      return Done;
+    return ShouldWait;
   }
 
   uint32_t size_to_pass = size;