[flutter_tools] wire up native-null-assertions for flutter web (#71618)

packages/flutter_tools/lib/src/device.dart

diff --git a/packages/flutter_tools/lib/src/device.dart b/packages/flutter_tools/lib/src/device.dart
index 53932d7..019c129 100644
--- a/packages/flutter_tools/lib/src/device.dart
+++ b/packages/flutter_tools/lib/src/device.dart
@@ -863,6 +863,7 @@
     this.vmserviceOutFile,
     this.fastStart = false,
     this.nullAssertions = false,
+    this.nativeNullAssertions = false,
    }) : debuggingEnabled = true;
 
   DebuggingOptions.disabled(this.buildInfo, {
@@ -897,7 +898,8 @@
       vmserviceOutFile = null,
       fastStart = false,
       webEnableExpressionEvaluation = false,
-      nullAssertions = false;
+      nullAssertions = false,
+      nativeNullAssertions = false;
 
   final bool debuggingEnabled;
 
@@ -947,6 +949,12 @@
 
   final bool nullAssertions;
 
+  /// Additional null runtime checks inserted for web applications.
+  ///
+  /// See also:
+  ///   * https://github.com/dart-lang/sdk/blob/master/sdk/lib/html/doc/NATIVE_NULL_ASSERTIONS.md
+  final bool nativeNullAssertions;
+
   bool get hasObservatoryPort => hostVmServicePort != null;
 }