Use a single file for app snapshots.

runtime/bin/file_macos.cc

 // Copyright (c) 2012, 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_MACOS)
 
 #include "bin/file.h"
 
 #include <copyfile.h>  // NOLINT
@@ skipping 62 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) {
   ASSERT(handle_->fd() >= 0);
-  intptr_t length = Length();
-  void* addr = mmap(0, length,
-                    PROT_READ | PROT_EXEC, MAP_PRIVATE,
-                    handle_->fd(), 0);
+  int prot = PROT_NONE;
+  switch (type) {
+    case kReadOnly:
+      prot = PROT_READ;
+      break;
+    case kReadExecute:
+      prot = PROT_READ | PROT_EXEC;
+      break;
+    default:
+      return NULL;
+  }
+  void* addr = mmap(NULL, length, prot, MAP_PRIVATE,
+                    handle_->fd(), position);
   if (addr == MAP_FAILED) {
-    *len = -1;
-  } else {
-    *len = length;
+    return NULL;
   }
   return addr;
 }
 
 
 int64_t File::Read(void* buffer, int64_t num_bytes) {
   ASSERT(handle_->fd() >= 0);
   return TEMP_FAILURE_RETRY(read(handle_->fd(), buffer, num_bytes));
 }
 
@@ skipping 380 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_MACOS)