Eliminate Dart 1 support from DevFS (#21404)

Dart 1 is no longer supported in Flutter. Hot reload now always occurs
via kernel file updates (plus any asset bundle changes).

packages/flutter_tools/lib/src/devfs.dart

@@ -426,10 +426,9 @@ class DevFS {
     await _scanDirectory(rootDirectory,
                          recursive: true,
                          fileFilter: fileFilter);
-    final bool previewDart2 = generator != null;
     if (fs.isFileSync(_packagesFilePath)) {
       printTrace('Scanning package files');
-      await _scanPackages(fileFilter, previewDart2);
+      await _scanPackages(fileFilter);
     }
     if (bundle != null) {
       printTrace('Scanning asset files');
@@ -480,12 +479,11 @@ class DevFS {
           assetPathsToEvict.add(archivePath);
       }
     });
-    if (previewDart2) {
-      // We run generator even if [dirtyEntries] was empty because we want
-      // to keep logic of accepting/rejecting generator's output simple:
-      // we must accept/reject generator's output after every [update] call.
-      // Incremental run with no changes is supposed to be fast (considering
-      // that it is initiated by user key press).
+    // We run generator even if [dirtyEntries] was empty because we want to
+    // keep logic of accepting/rejecting generator's output simple: we must
+    // accept/reject generator's output after every [update] call.  Incremental
+    // run with no changes is supposed to be fast (considering that it is
+    // initiated by user key press).
     final List<String> invalidatedFiles = <String>[];
     final Set<Uri> filesUris = new Set<Uri>();
     for (Uri uri in dirtyEntries.keys.toList()) {
@@ -505,22 +503,24 @@ class DevFS {
     if (fullRestart) {
       generator.reset();
     }
-      final CompilerOutput compilerOutput =
-          await generator.recompile(mainPath, invalidatedFiles,
+    final CompilerOutput compilerOutput = await generator.recompile(
+      mainPath,
+      invalidatedFiles,
       outputPath:  dillOutputPath ?? fs.path.join(getBuildDirectory(), 'app.dill'),
-              packagesFilePath : _packagesFilePath);
+      packagesFilePath : _packagesFilePath,
+    );
     final String compiledBinary = compilerOutput?.outputFilename;
     if (compiledBinary != null && compiledBinary.isNotEmpty) {
-        final Uri entryUri = fs.path.toUri(projectRootPath != null ?
-            fs.path.relative(pathToReload, from: projectRootPath):
-            pathToReload);
+      final Uri entryUri = fs.path.toUri(projectRootPath != null
+        ? fs.path.relative(pathToReload, from: projectRootPath)
+        : pathToReload,
+      );
       if (!dirtyEntries.containsKey(entryUri)) {
         final DevFSFileContent content = new DevFSFileContent(fs.file(compiledBinary));
         dirtyEntries[entryUri] = content;
         numBytes += content.size;
       }
     }
-    }
     if (dirtyEntries.isNotEmpty) {
       printTrace('Updating files');
       if (_httpWriter != null) {
@@ -697,7 +697,7 @@ class DevFS {
     );
   }
 
-  Future<Null> _scanPackages(Set<String> fileFilter, bool previewDart2) async {
+  Future<Null> _scanPackages(Set<String> fileFilter) async {
     StringBuffer sb;
     final PackageMap packageMap = new PackageMap(_packagesFilePath);
 
@@ -730,22 +730,6 @@ class DevFS {
         sb.writeln('$packageName:$directoryUriOnDevice');
       }
     }
-    if (previewDart2) {
-      // When in previewDart2 mode we don't update .packages-file entry
-      // so actual file will get invalidated in frontend.
-      // We don't need to synthesize device-correct .packages file because
-      // it is not going to be used on the device anyway - compilation
-      // is done on the host.
-      return;
-    }
-    if (sb != null) {
-      final DevFSContent content = _entries[fs.path.toUri('.packages')];
-      if (content is DevFSStringContent && content.string == sb.toString()) {
-        content._exists = true;
-        return;
-      }
-      _entries[fs.path.toUri('.packages')] = new DevFSStringContent(sb.toString());
-    }
   }
 }
 /// Converts a platform-specific file path to a platform-independent Uri path.