Clean up various ways we find paths in pub.

sdk/lib/_internal/dartdoc/lib/src/dartdoc/utils.dart

Index: sdk/lib/_internal/dartdoc/lib/src/dartdoc/utils.dart
diff --git a/sdk/lib/_internal/dartdoc/lib/src/dartdoc/utils.dart b/sdk/lib/_internal/dartdoc/lib/src/dartdoc/utils.dart
index 02b7de7db648e0c9f37d85aae61b03361c4913ed..929f6da382b02f88c1bc01e12230aa0bdf88ac9b 100644
--- a/sdk/lib/_internal/dartdoc/lib/src/dartdoc/utils.dart
+++ b/sdk/lib/_internal/dartdoc/lib/src/dartdoc/utils.dart
@@ -117,17 +117,28 @@ String fileUriToPath(Uri uri) {
   if (uri.scheme != 'file') {
     throw new ArgumentError("Uri $uri must have scheme 'file:'.");
   }
-  if (Platform.operatingSystem != 'windows') return pathos.normalize(uri.path);
-  return pathos.normalize(uri.path.replaceFirst("/", "").replaceAll("/", "\\"));
+  if (Platform.operatingSystem != 'windows') return uri.path;
+  if (uri.path.startsWith("/")) {
+    // Drive-letter paths look like "file:///C:/path/to/file". The replaceFirst
+    // removes the extra initial slash.
+    return uri.path.replaceFirst("/", "").replaceAll("/", "\\");
+  } else {
+    // Network paths look like "file://hostname/path/to/file".
+    return "\\\\${uri.path.replaceAll("/", "\\")}";
+  }
 }
 
 /** Converts a local path string to a `file:` [Uri]. */
-Uri pathToFileUri(String path) {
-  path = pathos.absolute(path);
+Uri pathToFileUri(String pathString) {
+  pathString = pathos.absolute(pathString);
   if (Platform.operatingSystem != 'windows') {
-    return Uri.parse('file://$path');
+    return Uri.parse('file://$pathString');
+  } else if (pathos.rootPrefix(path).startsWith('\\\\')) {
+    // Network paths become "file://hostname/path/to/file".
+    return Uri.parse('file:${pathString.replaceAll("\\", "/")}');
   } else {
-    return Uri.parse('file:///${path.replaceAll("\\", "/")}');
+    // Drive-letter paths become "file:///C:/path/to/file".
+    return Uri.parse('file:///${pathString.replaceAll("\\", "/")}');
   }
 }