fix spelling in core libraries

sdk/lib/io/stdio.dart

Index: sdk/lib/io/stdio.dart
diff --git a/sdk/lib/io/stdio.dart b/sdk/lib/io/stdio.dart
index 35560a9ff2d5d1759e0509b6e6677df0cf18ea12..2a878484efb45e6e96c246e1ec3d6a337335da51 100644
--- a/sdk/lib/io/stdio.dart
+++ b/sdk/lib/io/stdio.dart
@@ -51,7 +51,7 @@ class Stdin extends _StdStream implements Stream<List<int>> {
    *
    * If end-of-file is reached after any bytes have been read from stdin,
    * that data is returned.
-   * Returns `null` if no bytes preceeded the end of input.
+   * Returns `null` if no bytes preceded the end of input.
    */
   String readLineSync({Encoding encoding: SYSTEM_ENCODING,
                        bool retainNewlines: false}) {
@@ -86,7 +86,7 @@ class Stdin extends _StdStream implements Stream<List<int>> {
         line.add(byte);
       }
     } else {
-      // Case having to hande CR LF as a single unretained line terminator.
+      // Case having to handel CR LF as a single unretained line terminator.
       outer: while (true) {
         int byte = readByteSync();
         if (byte == LF) break;