Implement a MOJO_READ_DATA_FLAG_PEEK flag for data pipes.

mojo/edk/system/data_pipe.cc

Index: mojo/edk/system/data_pipe.cc
diff --git a/mojo/edk/system/data_pipe.cc b/mojo/edk/system/data_pipe.cc
index e9c490359c00de9b063ab7e0596cf346484c8308..e9525bc17a1eda5038a092665b9180189743f371 100644
--- a/mojo/edk/system/data_pipe.cc
+++ b/mojo/edk/system/data_pipe.cc
@@ -260,7 +260,8 @@ void DataPipe::ConsumerClose() {
 
 MojoResult DataPipe::ConsumerReadData(UserPointer<void> elements,
                                       UserPointer<uint32_t> num_bytes,
-                                      bool all_or_none) {
+                                      bool all_or_none,
+                                      bool peek) {
   base::AutoLock locker(lock_);
   DCHECK(has_local_consumer_no_lock());
 
@@ -279,7 +280,7 @@ MojoResult DataPipe::ConsumerReadData(UserPointer<void> elements,
   HandleSignalsState old_producer_state =
       ProducerGetHandleSignalsStateImplNoLock();
   MojoResult rv = ConsumerReadDataImplNoLock(
-      elements, num_bytes, max_num_bytes_to_read, min_num_bytes_to_read);
+      elements, num_bytes, max_num_bytes_to_read, min_num_bytes_to_read, peek);
   HandleSignalsState new_producer_state =
       ProducerGetHandleSignalsStateImplNoLock();
   if (!new_producer_state.equals(old_producer_state))