Add Socket::ReadIfReady()

net/socket/socket.h

Index: net/socket/socket.h
diff --git a/net/socket/socket.h b/net/socket/socket.h
index cda54063f3059e76726c896b5e6ae87508a5f483..8f5fed6dea08a65799468a23e1328a73d7af7a12 100644
--- a/net/socket/socket.h
+++ b/net/socket/socket.h
@@ -7,6 +7,7 @@
 
 #include <stdint.h>
 
+#include "base/feature_list.h"
 #include "net/base/completion_callback.h"
 #include "net/base/net_export.h"
 
@@ -17,6 +18,9 @@ class IOBuffer;
 // Represents a read/write socket.
 class NET_EXPORT Socket {
  public:
+  // Name of the field trial for using ReadyIfReady() instead of Read().
+  static const base::Feature kReadIfReadyExperiment;
+
   virtual ~Socket() {}
 
   // Reads data, up to |buf_len| bytes, from the socket.  The number of bytes
@@ -33,6 +37,19 @@ class NET_EXPORT Socket {
   virtual int Read(IOBuffer* buf, int buf_len,
                    const CompletionCallback& callback) = 0;
 
+  // Reads data, up to |buf_len| bytes, into |buf| without blocking. Default
+  // implementation returns ERR_READ_IF_READY_NOT_IMPLEMENTED. Caller should
+  // fall back to Read() if receives ERR_READ_IF_READY_NOT_IMPLEMENTED.
+  // Upon synchronous completion, returns the number of bytes read, or 0 on EOF,
+  // or an error code if an error happens. If read cannot be completed
+  // synchronously, returns ERR_IO_PENDING and does not hold on to |buf|.
+  // |callback| will be invoked with OK when data can be read, at which point,
+  // caller can call ReadIfReady() again. If an error occurs asynchronously,
+  // |callback| will be invoked with the error code.
+  virtual int ReadIfReady(IOBuffer* buf,
+                          int buf_len,
+                          const CompletionCallback& callback);
+
   // Writes data, up to |buf_len| bytes, to the socket.  Note: data may be
   // written partially.  The number of bytes written is returned, or an error
   // is returned upon failure.  ERR_SOCKET_NOT_CONNECTED should be returned if