dart:platform | Remove isWindows, isLinux, isAndroid, isMacOS from dart:platform.

sdk/lib/platform/platform.dart

Index: sdk/lib/platform/platform.dart
diff --git a/sdk/lib/platform/platform.dart b/sdk/lib/platform/platform.dart
index 68430a149bac46b79fa4e08bf74896dcce9d46ee..ee8658eba140d38e776204c8d78db1338a50ed05 100644
--- a/sdk/lib/platform/platform.dart
+++ b/sdk/lib/platform/platform.dart
@@ -19,6 +19,10 @@ external int get numberOfProcessors;
 /**
  * The path separator used on the platform to separate
  * components in file paths.
+ *
+ * Returns null if the path separator is unknown or not valid.
+ *
+ * Supported on the standalone Dart executable and on dart2js.
  */
 external String get pathSeparator;
 
@@ -49,28 +53,6 @@ external String get localHostname;
 external String get version;
 
 /**
- * True if the operating system is Linux.
- */
-// TODO(6997): Replace with bool get isLinux => operatingSystem == 'linux'
-// when issue with patched top-level functions is fixed.
-external bool get isLinux;
-
-/**
- * True if the operating system is Mac OS.
- */
-external bool get isMacOS;
-
-/**
- * True if the operating system is Windows.
- */
-external bool get isWindows;
-
-/**
- * True if the operating system is Android.
- */
-external bool get isAndroid;
-
-/**
  * The environment for this instance of the platform.
  *
  * If environment variables are not supported on this platform, or not