Change Mac OS to OS X in dart:io dartdoc

sdk/lib/io/file_system_entity.dart

Index: sdk/lib/io/file_system_entity.dart
diff --git a/sdk/lib/io/file_system_entity.dart b/sdk/lib/io/file_system_entity.dart
index 5c15c1c8c87d99906fe76572e1474861de86d72f..fe0b18826d3e026d2090a1abe6856aff3f56f348 100644
--- a/sdk/lib/io/file_system_entity.dart
+++ b/sdk/lib/io/file_system_entity.dart
@@ -273,7 +273,7 @@ abstract class FileSystemEntity {
    *
    * [resolveSymbolicLinks] uses the operating system's native
    * file system API to resolve the path, using the `realpath` function
-   * on linux and Mac OS, and the `GetFinalPathNameByHandle` function on
+   * on linux and OS X, and the `GetFinalPathNameByHandle` function on
    * Windows. If the path does not point to an existing file system object,
    * `resolveSymbolicLinks` throws a `FileSystemException`.
    *
@@ -313,7 +313,7 @@ abstract class FileSystemEntity {
    *
    * [resolveSymbolicLinksSync] uses the operating system's native
    * file system API to resolve the path, using the `realpath` function
-   * on linux and Mac OS, and the `GetFinalPathNameByHandle` function on
+   * on linux and OS X, and the `GetFinalPathNameByHandle` function on
    * Windows. If the path does not point to an existing file system object,
    * `resolveSymbolicLinksSync` throws a `FileSystemException`.
    *
@@ -418,7 +418,7 @@ abstract class FileSystemEntity {
    *     files and directories. Recursive watching is not supported.
    *     Note: When watching files directly, delete events might not happen
    *     as expected.
-   *   * `Mac OS`: Uses `FSEvents`. The implementation supports watching both
+   *   * `OS X`: Uses `FSEvents`. The implementation supports watching both
    *     files and directories. Recursive watching is supported.
    *
    * The system will start listening for events once the returned [Stream] is
@@ -529,7 +529,7 @@ abstract class FileSystemEntity {
   /**
    * Test if [watch] is supported on the current system.
    *
-   * Mac OS 10.6 and below is not supported.
+   * OS X 10.6 and below is not supported.
    */
   static bool get isWatchSupported => _FileSystemWatcher.isSupported;