Fix fromEnvironment when called from isolates.

runtime/vm/dart_api_impl.h

Index: runtime/vm/dart_api_impl.h
diff --git a/runtime/vm/dart_api_impl.h b/runtime/vm/dart_api_impl.h
index 2f10f43388dff386593b35a404bc81d2ee234e2b..3a5cf64db628b42fb5b7d3f75fc6275a92deacc8 100644
--- a/runtime/vm/dart_api_impl.h
+++ b/runtime/vm/dart_api_impl.h
@@ -109,6 +109,20 @@ const char* CanonicalFunction(const char* func);
 
 class Api : AllStatic {
  public:
+  // Create on the stack to provide a new throw-safe api scope.
+  class Scope : public StackResource {
+   public:
+    explicit Scope(Isolate* isolate) : StackResource(isolate) {
+      Dart_EnterScope();
+    }
+    ~Scope() {
+      Dart_ExitScope();
+    }
+
+   private:
+    DISALLOW_COPY_AND_ASSIGN(Scope);
+  };
+
   // Creates a new local handle.
   static Dart_Handle NewHandle(Isolate* isolate, RawObject* raw);