Fix filtering of emulator list

`flutter emulators nexus` will now return only those that'd match (eg. same things that `flutter emulators --start nexus` would match).

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

@@ -37,13 +37,17 @@ class EmulatorsCommand extends FlutterCommand {
     if (argResults.wasParsed('start')) {
       await _startEmulator(argResults['start']);
     } else {
-      await _listEmulators();
+      final String searchText =
+          argResults.rest != null && argResults.rest.isNotEmpty
+              ? argResults.rest.first
+              : null;
+      await _listEmulators(searchText);
     }
   }
 
   Future<Null> _startEmulator(String id) async {
     final List<Emulator> emulators =
-        await emulatorManager.getEmulatorsById(id).toList();
+        await emulatorManager.getEmulatorsMatching(id).toList();
 
     if (emulators.isEmpty) {
       printStatus("No emulator found that matches '$id'.");
@@ -55,9 +59,11 @@ class EmulatorsCommand extends FlutterCommand {
     }
   }
 
-  Future<Null> _listEmulators() async {
+  Future<Null> _listEmulators(String searchText) async {
     final List<Emulator> emulators =
-        await emulatorManager.getAllAvailableEmulators().toList();
+        searchText == null
+        ? await emulatorManager.getAllAvailableEmulators().toList()
+        : await emulatorManager.getEmulatorsMatching(searchText).toList();
 
     if (emulators.isEmpty) {
       printStatus('No emulators available.\n\n'

packages/flutter_tools/lib/src/emulator.dart

@@ -24,15 +24,15 @@ class EmulatorManager {
 
   final List<EmulatorDiscovery> _emulatorDiscoverers = <EmulatorDiscovery>[];
 
-  Stream<Emulator> getEmulatorsById(String emulatorId) async* {
+  Stream<Emulator> getEmulatorsMatching(String searchText) async* {
     final List<Emulator> emulators = await getAllAvailableEmulators().toList();
-    emulatorId = emulatorId.toLowerCase();
+    searchText = searchText.toLowerCase();
     bool exactlyMatchesEmulatorId(Emulator emulator) =>
-        emulator.id?.toLowerCase() == emulatorId ||
-        emulator.name?.toLowerCase() == emulatorId;
+        emulator.id?.toLowerCase() == searchText ||
+        emulator.name?.toLowerCase() == searchText;
     bool startsWithEmulatorId(Emulator emulator) =>
-        emulator.id?.toLowerCase()?.startsWith(emulatorId) == true ||
-        emulator.name?.toLowerCase()?.startsWith(emulatorId) == true;
+        emulator.id?.toLowerCase()?.startsWith(searchText) == true ||
+        emulator.name?.toLowerCase()?.startsWith(searchText) == true;
 
     final Emulator exactMatch = emulators.firstWhere(
         exactlyMatchesEmulatorId, orElse: () => null);

packages/flutter_tools/test/emulator_test.dart

@@ -26,7 +26,7 @@ void main() {
       final EmulatorManager emulatorManager = new TestEmulatorManager(emulators);
 
       Future<Null> expectEmulator(String id, List<Emulator> expected) async {
-        expect(await emulatorManager.getEmulatorsById(id).toList(), expected);
+        expect(await emulatorManager.getEmulatorsMatching(id).toList(), expected);
       }
       expectEmulator('Nexus_5', <Emulator>[emulator1]);
       expectEmulator('Nexus_5X', <Emulator>[emulator2]);