Introduce Dart_SetVMFlags API function.

runtime/bin/gen_snapshot.cc

Index: runtime/bin/gen_snapshot.cc
diff --git a/runtime/bin/gen_snapshot.cc b/runtime/bin/gen_snapshot.cc
index b0358bf441993d25970376800275b5a089138bdd..f15ba64fd443321e06a36e51c478cdb74bc01261 100644
--- a/runtime/bin/gen_snapshot.cc
+++ b/runtime/bin/gen_snapshot.cc
@@ -254,11 +254,8 @@ int main(int argc, char** argv) {
     return 255;
   }
 
-  // Initialize the Dart VM (TODO(asiva) - remove const_cast once
-  // dart API is fixed to take a const char** in Dart_Initialize).
-  Dart_Initialize(vm_options.count(),
-                  vm_options.arguments(),
-                  SnapshotCreateCallback);
+  Dart_SetVMFlags(vm_options.count(), vm_options.arguments());
+  Dart_Initialize(SnapshotCreateCallback);
 
   // Create an isolate. As a side effect, SnapshotCreateCallback
   // gets called, which loads the script (if one is specified), its libraries