Document that Uri.scheme and Uri.host are lower-case.

sdk/lib/core/uri.dart

Index: sdk/lib/core/uri.dart
diff --git a/sdk/lib/core/uri.dart b/sdk/lib/core/uri.dart
index de2c38bbf8ab6558ca07e00c739b26f399b76b8f..d021b31a9b0d820e2a83bbbe6949c6ad936e0d13 100644
--- a/sdk/lib/core/uri.dart
+++ b/sdk/lib/core/uri.dart
@@ -30,6 +30,9 @@ class Uri {
    * Returns the scheme component.
    *
    * Returns the empty string if there is no scheme component.
+   *
+   * A URI scheme is case insensitive.
+   * The returned scheme is canonicalized to lowercase letters.
    */
   // We represent the missing scheme as an empty string.
   // A valid scheme cannot be empty.
@@ -74,6 +77,10 @@ class Uri {
    *
    * If the host is an IP version 6 address, the surrounding `[` and `]` is
    * removed.
+   *
+   * The host string is case-insensitive.
+   * The returned host name is canonicalized to lower-case
+   * with upper-case percent-escapes.
    */
   String get host {
     if (_host == null) return "";