Pass environment defines to compile flutter platform step. (#8412)

* Pass environment defines to the compiler

* Remove non-strong platform target

lib/snapshot/BUILD.gn

@@ -231,23 +231,6 @@ source_set("snapshot") {
             get_target_outputs(":platform_strong_dill_linkable")
 }
 
-compile_platform("non_strong_platform") {
-  single_root_scheme = "org-dartlang-sdk"
-  single_root_base = rebase_path("../../../")
-  libraries_specification_uri =
-      "org-dartlang-sdk:///flutter/lib/snapshot/libraries.json"
-
-  outputs = [
-    "$root_out_dir/flutter_patched_sdk/platform.dill",
-    "$root_out_dir/flutter_patched_sdk/vm_outline.dill",
-  ]
-
-  args = [
-    "--target=flutter",
-    "dart:core",
-  ]
-}
-
 compile_platform("strong_platform") {
   single_root_scheme = "org-dartlang-sdk"
   single_root_base = rebase_path("../../../")
@@ -259,8 +242,13 @@ compile_platform("strong_platform") {
     "$root_out_dir/flutter_patched_sdk/vm_outline_strong.dill",
   ]
 
+  is_runtime_mode_release = flutter_runtime_mode == "release"
+  allow_causal_async_stacks = !is_runtime_mode_release
   args = [
     "--target=flutter",
+    "-Ddart.vm.product=$is_runtime_mode_release",
+    "-Ddart.developer.causal_async_stacks=$allow_causal_async_stacks",
+    "-Ddart.isVM=true",
     "dart:core",
   ]
 }
@@ -275,7 +263,6 @@ if (is_fuchsia || is_fuchsia_host) {
 } else {
   group("kernel_platform_files") {
     public_deps = [
-      ":non_strong_platform",
       ":strong_platform",
     ]
   }