Fuchsia: Build standalone VM. Make it run "Hello, World!".

runtime/bin/vmservice_impl.cc

Index: runtime/bin/vmservice_impl.cc
diff --git a/runtime/bin/vmservice_impl.cc b/runtime/bin/vmservice_impl.cc
index cfb05caf00cfcf5534e207ba16e0fa0eddf44584..d85186326f9436e679bb8999f8da1882a55062c1 100644
--- a/runtime/bin/vmservice_impl.cc
+++ b/runtime/bin/vmservice_impl.cc
@@ -256,6 +256,16 @@ bool VmService::Setup(const char* server_ip,
       Dart_SetField(library, DartUtils::NewString("_isWindows"), is_windows);
   SHUTDOWN_ON_ERROR(result);
 
+  // Are we running on Fuchsia?
+#if defined(TARGET_OS_FUCHSIA)
+  Dart_Handle is_fuchsia = Dart_True();
+#else
+  Dart_Handle is_fuchsia = Dart_False();
+#endif
+  result =
+      Dart_SetField(library, DartUtils::NewString("_isFuchsia"), is_fuchsia);
+  SHUTDOWN_ON_ERROR(result);
+
   // Get _getWatchSignalInternal from dart:io.
   Dart_Handle dart_io_str = Dart_NewStringFromCString(DartUtils::kIOLibURL);
   SHUTDOWN_ON_ERROR(dart_io_str);