Remove support for "all or none" two-phase data pipe read/write.

mojo/public/go/system/system.go

 // Copyright 2015 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.
 
 package system
 
 // This interface wraps the "raw" mojo system entry points. This has no
 // dependencies on other types in this package so it can be implemented
 // by code that doesn't depend on this package.
 type MojoSystem interface {
         // Shared buffer
         CreateSharedBuffer(flags uint32, numBytes uint64) (result uint32, handle uint32)
         DuplicateBufferHandle(handle uint32, flags uint32) (result uint32, dupHandle uint32)
         // After a successful MapBuffer call, the caller must pass the same slice value to UnmapBuffer to release
         // the underlying memory segment.
         MapBuffer(handle uint32, offset, numBytes uint64, flags uint32) (result uint32, buf []byte)
         UnmapBuffer(buf []byte) (result uint32)
 
         // Data pipe
         CreateDataPipe(flags, elementNumBytes, capacityNumBytes uint32) (result uint32, producerHandle, consumerHandle uint32)
         CreateDataPipeWithDefaultOptions() (result uint32, producerHandle, consumerHandle uint32)
         WriteData(producerHandle uint32, buf []byte, flags uint32) (result uint32, bytesWritten uint32)
-        BeginWriteData(producerHandle uint32, numBytes uint32, flags uint32) (result uint32, buf []byte)
+        BeginWriteData(producerHandle uint32, flags uint32) (result uint32, buf []byte)
         EndWriteData(producerHandle uint32, numBytesWritten uint32) (result uint32)
 
         ReadData(consumerHandle, flags uint32) (result uint32, buf []byte)
-        BeginReadData(consumerHandle uint32, numBytes uint32, flags uint32) (result uint32, buf []byte)
+        BeginReadData(consumerHandle uint32, flags uint32) (result uint32, buf []byte)
         EndReadData(consumerHandle uint32, numBytesRead uint32) (result uint32)
 
         // Time
         GetTimeTicksNow() (timestamp uint64)
 
         // Close a handle
         Close(handle uint32) (result uint32)
 
         // Waiting
         Wait(handle uint32, signals uint32, deadline uint64) (result uint32, satisfiedSignals, satisfiableSignals uint32)
         WaitMany(handles []uint32, signals []uint32, deadline uint64) (result uint32, index int, satisfiedSignals, satisfiableSignals []uint32)
 
         // Message pipe
         CreateMessagePipe(flags uint32) (result uint32, handle0, handle1 uint32)
         WriteMessage(handle uint32, bytes []byte, handles []uint32, flags uint32) (result uint32)
         ReadMessage(handle uint32, flags uint32) (result uint32, buf []byte, handles []uint32)
 }
 
 var sysImpl MojoSystem