Simplify the canonicalization of dart-ext uris.

runtime/bin/builtin.dart

Index: runtime/bin/builtin.dart
diff --git a/runtime/bin/builtin.dart b/runtime/bin/builtin.dart
index f0c0cdcf666adcbed7c9b14d0727df9ec4c35e7a..6b16d994551827de5ae466d623cc1eaafb690ffd 100644
--- a/runtime/bin/builtin.dart
+++ b/runtime/bin/builtin.dart
@@ -702,13 +702,7 @@ String _resolveUri(String base, String userString) {
     _log('Resolving: $userString from $base');
   }
   var baseUri = Uri.parse(base);
-  var result;
-  if (userString.startsWith(_DART_EXT)) {
-    var uri = userString.substring(_DART_EXT.length);
-    result = '$_DART_EXT${baseUri.resolve(uri)}';
-  } else {
-    result = baseUri.resolve(userString).toString();
-  }
+  var result = baseUri.resolve(userString).toString();
   if (_traceLoading) {
     _log('Resolved $userString in $base to $result');
   }
@@ -831,10 +825,6 @@ String _resolveInWorkingDirectory(String fileName) {
 }
 
 
-// Handling of dart-ext loading.
-// Dart native extension scheme.
-const _DART_EXT = 'dart-ext:';
-
 // Returns either a file path or a URI starting with http[s]:, as a String.
 String _filePathFromUri(String userUri) {
   var uri = Uri.parse(userUri);
@@ -864,42 +854,19 @@ String _filePathFromUri(String userUri) {
 }
 
 
-// Embedder Entrypoint:
-// When loading an extension the embedder calls this method to get the
-// different components.
-// Returns the directory part, the filename part, and the name
-// of a native extension URL as a list [directory, filename, name].
-// The directory part is either a file system path or an HTTP(S) URL.
-// The filename part is the extension name, with the platform-dependent
-// prefixes and extensions added.
-_extensionPathFromUri(String userUri) {
+// Embedder Entrypoint.
+_libraryFilePath(String libraryUri) {
   if (!_setupCompleted) {
     _setupHooks();
   }
-  if (!userUri.startsWith(_DART_EXT)) {
-    throw 'Unexpected internal error: Extension URI $userUri missing dart-ext:';
-  }
-  userUri = userUri.substring(_DART_EXT.length);
-
-  if (userUri.contains('\\')) {
-    throw 'Unexpected internal error: Extension URI $userUri contains \\';
-  }
-
-  String name;
-  String path;  // Will end in '/'.
-  int index = userUri.lastIndexOf('/');
+  int index = libraryUri.lastIndexOf('/');
+  var path;
   if (index == -1) {
-    name = userUri;
     path = './';
-  } else if (index == userUri.length - 1) {
-    throw 'Extension name missing in $extensionUri';
   } else {
-    name = userUri.substring(index + 1);
-    path = userUri.substring(0, index + 1);
+    path = libraryUri.substring(0, index + 1);
   }
-  path = _filePathFromUri(path);
-
-  return [path, name];
+  return _filePathFromUri(path);
 }