Allocate the profiler sample buffer and zone segments with virtual memory instead of malloc.

runtime/vm/virtual_memory_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 "vm/globals.h"
 #if defined(HOST_OS_FUCHSIA)
 
 #include "vm/virtual_memory.h"
 
 #include <magenta/process.h>
@@ skipping 135 matching lines @@
 
 uword VirtualMemory::page_size_ = 0;
 
 
 void VirtualMemory::InitOnce() {
   page_size_ = getpagesize();
 }
 
 
 VirtualMemory* VirtualMemory::ReserveInternal(intptr_t size) {
+  ASSERT(Utils::IsAligned(size, page_size_));
   mx_handle_t vmar = MX_HANDLE_INVALID;
   uword addr = 0;
   const uint32_t flags = MX_VM_FLAG_COMPACT | MX_VM_FLAG_CAN_MAP_SPECIFIC |
                          MX_VM_FLAG_CAN_MAP_READ | MX_VM_FLAG_CAN_MAP_WRITE |
                          MX_VM_FLAG_CAN_MAP_EXECUTE;
   mx_status_t status =
       mx_vmar_allocate(mx_vmar_root_self(), 0, size, flags, &vmar, &addr);
   if (status != MX_OK) {
     LOG_ERR("mx_vmar_allocate(size = %ld) failed: %s\n", size,
             mx_status_get_string(status));
@@ skipping 115 matching lines @@
     return false;
   }
   LOG_INFO("mx_vmar_protect(%lx, %lx, %x) success\n", page_address,
            end_address - page_address, prot);
   return true;
 }
 
 }  // namespace dart
 
 #endif  // defined(HOST_OS_FUCHSIA)