Mojo EDK: Introduce MojoQueryHandleSignalsState API

mojo/public/c/system/functions.h

Index: mojo/public/c/system/functions.h
diff --git a/mojo/public/c/system/functions.h b/mojo/public/c/system/functions.h
index 750a29ee0728c368c1ac8761f1129979ef0783b1..4dad70b21d6ebfe6c32b3ed7f43914292d967e47 100644
--- a/mojo/public/c/system/functions.h
+++ b/mojo/public/c/system/functions.h
@@ -46,6 +46,21 @@ MOJO_SYSTEM_EXPORT MojoTimeTicks MojoGetTimeTicksNow(void);
 // fail with |MOJO_RESULT_INVALID_ARGUMENT| if they happen after.
 MOJO_SYSTEM_EXPORT MojoResult MojoClose(MojoHandle handle);
 
+// Queries the last known signals state of a handle.
+//
+// Note that no guarantees can be made about the accuracy of the returned
+// signals state by the time this returns, as other threads in the system may
+// change the handle's state at any time. Use with appropriate discretion.
+//
+// Returns:
+//   |MOJO_RESULT_OK| on success. |*signals_state| is populated with the
+//       last known signals state of |handle|.
+//   |MOJO_RESULT_INVALID_ARGUMENT| if |handle| is not a valid handle or
+//       |signals_state| is null.
+MOJO_SYSTEM_EXPORT MojoResult
+MojoQueryHandleSignalsState(MojoHandle handle,
+                            struct MojoHandleSignalsState* signals_state);
+
 // Waits on the given handle until one of the following happens:
 //   - A signal indicated by |signals| is satisfied.
 //   - It becomes known that no signal indicated by |signals| will ever be