Use FileSystem.pathSeparator instead of Platform.pathSeparator (#7417)

packages/flutter_tools/lib/src/asset.dart

@@ -10,7 +10,6 @@ import 'package:path/path.dart' as path;
 import 'package:yaml/yaml.dart';
 
 import 'base/file_system.dart';
-import 'base/io.dart';
 import 'build_info.dart';
 import 'cache.dart';
 import 'dart/package_map.dart';
@@ -378,7 +377,7 @@ Map<_Asset, List<_Asset>> _parseAssets(
     return result;
 
   excludeDirs = excludeDirs.map(
-    (String exclude) => path.absolute(exclude) + Platform.pathSeparator).toList();
+    (String exclude) => path.absolute(exclude) + fs.pathSeparator).toList();
 
   if (manifestDescriptor.containsKey('assets')) {
     for (String asset in manifestDescriptor['assets']) {

packages/flutter_tools/lib/src/base/process.dart

@@ -5,6 +5,7 @@
 import 'dart:async';
 import 'dart:convert';
 
+import 'file_system.dart';
 import 'io.dart';
 import 'process_manager.dart';
 import '../globals.dart';
@@ -202,7 +203,7 @@ void _traceCommand(List<String> args, { String workingDirectory }) {
   if (workingDirectory == null)
     printTrace(argsText);
   else
-    printTrace("[$workingDirectory${Platform.pathSeparator}] $argsText");
+    printTrace("[$workingDirectory${fs.pathSeparator}] $argsText");
 }
 
 String _runWithLoggingSync(List<String> cmd, {

packages/flutter_tools/lib/src/base/utils.dart

@@ -93,7 +93,7 @@ String getElapsedAsMilliseconds(Duration duration) {
 /// Return a relative path if [fullPath] is contained by the cwd, else return an
 /// absolute path.
 String getDisplayPath(String fullPath) {
-  String cwd = fs.currentDirectory.path + Platform.pathSeparator;
+  String cwd = fs.currentDirectory.path + fs.pathSeparator;
   return fullPath.startsWith(cwd) ?  fullPath.substring(cwd.length) : fullPath;
 }
 

packages/flutter_tools/lib/src/commands/analyze_base.dart

@@ -8,7 +8,6 @@ import 'package:args/args.dart';
 import 'package:path/path.dart' as path;
 
 import '../base/file_system.dart';
-import '../base/io.dart';
 import '../base/utils.dart';
 import '../cache.dart';
 import '../globals.dart';
@@ -59,7 +58,7 @@ bool inRepo(List<String> fileList) {
   if (fileList == null || fileList.isEmpty)
     fileList = <String>[path.current];
   String root = path.normalize(path.absolute(Cache.flutterRoot));
-  String prefix = root + Platform.pathSeparator;
+  String prefix = root + fs.pathSeparator;
   for (String file in fileList) {
     file = path.normalize(path.absolute(file));
     if (file == root || file.startsWith(prefix))

packages/flutter_tools/lib/src/commands/build.dart

@@ -8,7 +8,6 @@ import 'package:meta/meta.dart';
 
 import '../base/common.dart';
 import '../base/file_system.dart';
-import '../base/io.dart';
 import '../base/utils.dart';
 import '../build_info.dart';
 import '../globals.dart';
@@ -88,7 +87,7 @@ class BuildCleanCommand extends FlutterCommand {
   @override
   Future<Null> runCommand() async {
     Directory buildDir = fs.directory(getBuildDirectory());
-    printStatus("Deleting '${buildDir.path}${Platform.pathSeparator}'.");
+    printStatus("Deleting '${buildDir.path}${fs.pathSeparator}'.");
 
     if (!buildDir.existsSync())
       return;

packages/flutter_tools/lib/src/commands/build_aot.dart

@@ -8,7 +8,6 @@ import 'package:path/path.dart' as path;
 
 import '../base/common.dart';
 import '../base/file_system.dart';
-import '../base/io.dart';
 import '../base/logger.dart';
 import '../base/process.dart';
 import '../base/utils.dart';
@@ -65,7 +64,7 @@ class BuildAotCommand extends BuildSubCommand {
     if (outputPath == null)
       throwToolExit(null);
 
-    printStatus('Built to $outputPath${Platform.pathSeparator}.');
+    printStatus('Built to $outputPath${fs.pathSeparator}.');
   }
 }