Don't use file-based part-of when part files are shared.

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
 // JavaScript objects [ECMA-262], DOMString [WEBIDL], Date [ECMA-262] or float
 // [WEBIDL]. However Arrays are only valid keys if every item in the array is
 // defined and is a valid key (i.e. sparse arrays can not be valid keys) and if
 // the Array doesn't directly or indirectly contain itself. Any non-numeric
 // properties are ignored, and thus does not affect whether the Array is a valid
 // key. Additionally, if the value is of type float, it is only a valid key if
 // it is not NaN, and if the value is of type Date it is only a valid key if its
 // [[PrimitiveValue]] internal property, as defined by [ECMA-262], is not NaN."
 
 // What is required is to ensure that an Lists in the key are actually
 // JavaScript arrays, and any Dates are JavaScript Dates.
 
 // Conversions for Window.  These check if the window is the local
 // window, and if it's not, wraps or unwraps it with a secure wrapper.
 // We need to test for EventTarget here as well as it's a base type.
 // We omit an unwrapper for Window as no methods take a non-local
 // window as a parameter.
 
-part of "html_common.dart";
+part of html_common;
 
 /// Converts a Dart value into a JavaScript SerializedScriptValue.
 convertDartToNative_SerializedScriptValue(value) {
   return convertDartToNative_PrepareForStructuredClone(value);
 }
 
 /// Since the source object may be viewed via a JavaScript event listener the
 /// original may not be modified.
 convertNativeToDart_SerializedScriptValue(object) {
   return convertNativeToDart_AcceptStructuredClone(object, mustCopy: true);
@@ skipping 310 matching lines @@
 
 // We can get rid of this conversion if _TypedImageData implements the fields
 // with native names.
 convertDartToNative_ImageData(ImageData imageData) {
   if (imageData is _TypedImageData) {
     return JS('', '{data: #, height: #, width: #}', imageData.data,
         imageData.height, imageData.width);
   }
   return imageData;
 }