Fix static warnings in pkg/path.

pkg/path/lib/path.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.
 
 /// A comprehensive, cross-platform path manipulation library.
 ///
 /// ## Installing ##
 ///
 /// Use [pub][] to install this package. Add the following to your
 /// `pubspec.yaml` file.
@@ skipping 739 matching lines @@
 
     // Remove the root prefix, if any.
     var root = style.getRoot(path);
     var isRootRelative = style.getRelativeRoot(path) != null;
     if (root != null) path = path.substring(root.length);
 
     // Split the parts on path separators.
     var parts = [];
     var separators = [];
 
-    var firstSeparator = style.separatorPattern.firstMatch(path);
-    if (firstSeparator != null && firstSeparator.start == 0) {
+    var firstSeparator = style.separatorPattern.matchAsPrefix(path);
+    if (firstSeparator != null) {
       separators.add(firstSeparator[0]);
       path = path.substring(firstSeparator[0].length);
     } else {
       separators.add('');
     }
 
     var start = 0;
     for (var match in style.separatorPattern.allMatches(path)) {
       parts.add(path.substring(start, match.start));
       separators.add(match[0]);
@@ skipping 60 matching lines @@
   /// The [Pattern] that can be used to match the root prefix of a root-relative
   /// path in this style.
   ///
   /// This can be null to indicate that this style doesn't support root-relative
   /// paths.
   final Pattern relativeRootPattern = null;
 
   /// Gets the root prefix of [path] if path is absolute. If [path] is relative,
   /// returns `null`.
   String getRoot(String path) {
-    var match = rootPattern.firstMatch(path);
-    if (match != null) return match[0];
+    // TODO(rnystrom): Use firstMatch() when #7080 is fixed.
+    var matches = rootPattern.allMatches(path);
+    if (matches.isNotEmpty) return matches.first[0];
     return getRelativeRoot(path);
   }
 
   /// Gets the root prefix of [path] if it's root-relative.
   ///
   /// If [path] is relative or absolute and not root-relative, returns `null`.
   String getRelativeRoot(String path) {
     if (relativeRootPattern == null) return null;
-    var match = relativeRootPattern.firstMatch(path);
-    if (match == null) return null;
-    return match[0];
+    // TODO(rnystrom): Use firstMatch() when #7080 is fixed.
+    var matches = relativeRootPattern.allMatches(path);
+    if (matches.isEmpty) return null;
+    return matches.first[0];
   }
 
   /// Returns the path represented by [uri] in this style.
   String pathFromUri(Uri uri);
 
   /// Returns the URI that represents [path].
   ///
   /// Pathos will always path an absolute path for [path]. Relative paths are
   /// handled automatically by [Builder].
   Uri pathToUri(String path);
@@ skipping 258 matching lines @@
     // doesn't count.
     if (lastDot <= 0) return [file, ''];
 
     return [file.substring(0, lastDot), file.substring(lastDot)];
   }
 
   _ParsedPath clone() => new _ParsedPath(
       style, root, isRootRelative,
       new List.from(parts), new List.from(separators));
 }