Reapply "Use a single file for app snapshots."

runtime/bin/file_fuchsia.cc

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "platform/globals.h"
 #if defined(TARGET_OS_FUCHSIA)
 
 #include "bin/file.h"
 
 #include <errno.h>  // NOLINT
@@ skipping 57 matching lines @@
 intptr_t File::GetFD() {
   return handle_->fd();
 }
 
 
 bool File::IsClosed() {
   return handle_->fd() == kClosedFd;
 }
 
 
-void* File::MapExecutable(intptr_t* len) {
+void* File::Map(MapType type, int64_t position, int64_t length) {
   UNIMPLEMENTED();
   return NULL;
 }
 
 
 int64_t File::Read(void* buffer, int64_t num_bytes) {
   ASSERT(handle_->fd() >= 0);
   return NO_RETRY_EXPECTED(read(handle_->fd(), buffer, num_bytes));
 }
 
@@ skipping 354 matching lines @@
   return ((file_1_info.st_ino == file_2_info.st_ino) &&
           (file_1_info.st_dev == file_2_info.st_dev)) ?
       File::kIdentical :
       File::kDifferent;
 }
 
 }  // namespace bin
 }  // namespace dart
 
 #endif  // defined(TARGET_OS_FUCHSIA)