Implement a MOJO_READ_DATA_FLAG_PEEK flag for data pipes.

mojo/edk/system/data_pipe.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef MOJO_EDK_SYSTEM_DATA_PIPE_H_
 #define MOJO_EDK_SYSTEM_DATA_PIPE_H_
 
 #include <stdint.h>
 
 #include "base/macros.h"
@@ skipping 55 matching lines @@
   bool ProducerIsBusy() const;
 
   // These are called by the consumer dispatcher to implement its methods of
   // corresponding names.
   void ConsumerCancelAllWaiters();
   void ConsumerClose();
   // This does not validate its arguments, except to check that |*num_bytes| is
   // a multiple of |element_num_bytes_|.
   MojoResult ConsumerReadData(UserPointer<void> elements,
                               UserPointer<uint32_t> num_bytes,
-                              bool all_or_none);
+                              bool all_or_none,
+                              bool peek);
   MojoResult ConsumerDiscardData(UserPointer<uint32_t> num_bytes,
                                  bool all_or_none);
   MojoResult ConsumerQueryData(UserPointer<uint32_t> num_bytes);
   MojoResult ConsumerBeginReadData(UserPointer<const void*> buffer,
                                    UserPointer<uint32_t> buffer_num_bytes,
                                    bool all_or_none);
   MojoResult ConsumerEndReadData(uint32_t num_bytes_read);
   HandleSignalsState ConsumerGetHandleSignalsState();
   MojoResult ConsumerAddWaiter(Waiter* waiter,
                                MojoHandleSignals signals,
@@ skipping 26 matching lines @@
   // Note: A producer should not be writable during a two-phase write.
   virtual HandleSignalsState ProducerGetHandleSignalsStateImplNoLock()
       const = 0;
 
   virtual void ConsumerCloseImplNoLock() = 0;
   // |*num_bytes| will be a nonzero multiple of |element_num_bytes_|.
   virtual MojoResult ConsumerReadDataImplNoLock(
       UserPointer<void> elements,
       UserPointer<uint32_t> num_bytes,
       uint32_t max_num_bytes_to_read,
-      uint32_t min_num_bytes_to_read) = 0;
+      uint32_t min_num_bytes_to_read,
+      bool peek) = 0;
   virtual MojoResult ConsumerDiscardDataImplNoLock(
       UserPointer<uint32_t> num_bytes,
       uint32_t max_num_bytes_to_discard,
       uint32_t min_num_bytes_to_discard) = 0;
   // |*num_bytes| will be a nonzero multiple of |element_num_bytes_|.
   virtual MojoResult ConsumerQueryDataImplNoLock(
       UserPointer<uint32_t> num_bytes) = 0;
   virtual MojoResult ConsumerBeginReadDataImplNoLock(
       UserPointer<const void*> buffer,
       UserPointer<uint32_t> buffer_num_bytes,
@@ skipping 73 matching lines @@
   uint32_t producer_two_phase_max_num_bytes_written_;
   uint32_t consumer_two_phase_max_num_bytes_read_;
 
   DISALLOW_COPY_AND_ASSIGN(DataPipe);
 };
 
 }  // namespace system
 }  // namespace mojo
 
 #endif  // MOJO_EDK_SYSTEM_DATA_PIPE_H_