Add support for building the Dart VM for Android OS.

runtime/vm/virtual_memory_android.cc

Index: runtime/vm/virtual_memory_android.cc
diff --git a/runtime/vm/virtual_memory_linux.cc b/runtime/vm/virtual_memory_android.cc
similarity index 97%
copy from runtime/vm/virtual_memory_linux.cc
copy to runtime/vm/virtual_memory_android.cc
index 189c0fc4c9b6cd58d8ca3d2a27ffb73b50a027e7..74f43a294a540d9f60137836f05f34ef744570f9 100644
--- a/runtime/vm/virtual_memory_linux.cc
+++ b/runtime/vm/virtual_memory_android.cc
@@ -5,7 +5,6 @@
 #include "vm/virtual_memory.h"
 
 #include <sys/mman.h>
-#include <sys/unistd.h>
 #include <unistd.h>
 
 #include "platform/assert.h"
@@ -27,6 +26,7 @@ void VirtualMemory::InitOnce() {
 
 
 VirtualMemory* VirtualMemory::Reserve(intptr_t size) {
+  // TODO(4480): use ashmem instead of anonymous memory

[Emily Fortuna, 2012/08/08 01:28:37]

Generally the TODO messages contain a person's ldap, like
// TODO(jackpal): Use ashmem instead of anonymous memory.
(what's 4480? It's not dartbug.com/4480 -- I saw Charlie asked you to add this,
so disregard if this is the VM-team way of doing things and this makes sense to
them.)

[cshapiro, 2012/08/08 02:57:42]

I think this is just a simple transposition error.  The value in the TODO should
be 4408 not 4480.  You might already know this but we used this convention when
we moved from the internal repository to the public repository.

[jackpal, 2012/08/08 23:06:45]

Done.

   void* address = mmap(NULL, size, PROT_NONE,
                        MAP_PRIVATE | MAP_ANON | MAP_NORESERVE,
                        -1, 0);