Replace the now missing ContextAttributes with our previously Firefox-only _TypedContextAttributes

sdk/lib/html/html_common/conversions.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 
 // Conversions for IDBKey.
 //
 // Per http://www.w3.org/TR/IndexedDB/#key-construct
 //
 // "A value is said to be a valid key if it is one of the following types: Array
@@ skipping 248 matching lines @@
   convertNativeToDart_AcceptStructuredClone(object, {mustCopy: false}) {
     this.mustCopy = mustCopy;
     var copy = walk(object);
     return copy;
   }
 }
 
 // Conversions for ContextAttributes.
 //
 // On Firefox, the returned ContextAttributes is a plain object.
-class _TypedContextAttributes {
+class ContextAttributes {
   bool alpha;
   bool antialias;
   bool depth;
   bool premultipliedAlpha;
   bool preserveDrawingBuffer;
   bool stencil;
   bool failIfMajorPerformanceCaveat;
 
-  _TypedContextAttributes(this.alpha, this.antialias, this.depth,
+  ContextAttributes(this.alpha, this.antialias, this.depth,
       this.failIfMajorPerformanceCaveat, this.premultipliedAlpha,
       this.preserveDrawingBuffer, this.stencil);
 }
 
 convertNativeToDart_ContextAttributes(nativeContextAttributes) {
   // On Firefox the above test fails because ContextAttributes is a plain
   // object so we create a _TypedContextAttributes.
 
-  return new _TypedContextAttributes(
+  return new ContextAttributes(
       JS('var', '#.alpha', nativeContextAttributes),
       JS('var', '#.antialias', nativeContextAttributes),
       JS('var', '#.depth', nativeContextAttributes),
       JS('var', '#.failIfMajorPerformanceCaveat', nativeContextAttributes),
       JS('var', '#.premultipliedAlpha', nativeContextAttributes),
       JS('var', '#.preserveDrawingBuffer', nativeContextAttributes),
       JS('var', '#.stencil', nativeContextAttributes));
 }
 
 // Conversions for ImageData
@@ skipping 57 matching lines @@
 const String _serializedScriptValue =
     'num|String|bool|'
     'JSExtendableArray|=Object|'
     'Blob|File|NativeByteBuffer|NativeTypedData'
     // TODO(sra): Add Date, RegExp.
     ;
 const annotation_Creates_SerializedScriptValue =
     const Creates(_serializedScriptValue);
 const annotation_Returns_SerializedScriptValue =
     const Returns(_serializedScriptValue);