Add option to precache unsigned mac binaries. (#42376)

packages/flutter_tools/lib/src/cache.dart

diff --git a/packages/flutter_tools/lib/src/cache.dart b/packages/flutter_tools/lib/src/cache.dart
index 07c1b73..d173bdf 100644
--- a/packages/flutter_tools/lib/src/cache.dart
+++ b/packages/flutter_tools/lib/src/cache.dart
@@ -128,6 +128,9 @@
   // artifacts for the current platform.
   bool includeAllPlatforms = false;
 
+  // Whether to cache the unsigned mac binaries. Defaults to caching the signed binaries.
+  bool useUnsignedMacBinaries = false;
+
   static RandomAccessFile _lock;
   static bool _lockEnabled = true;
 
@@ -1101,12 +1104,14 @@
 
   @override
   Future<void> updateInner() {
-    if (!platform.isMacOS) {
+    if (!platform.isMacOS && !cache.includeAllPlatforms) {
       return Future<void>.value();
     }
-    final Uri archiveUri = Uri.parse('$_storageBaseUrl/flutter_infra/ios-usb-dependencies/$name/$version/$name.zip');
     return _downloadZipArchive('Downloading $name...', archiveUri, location);
   }
+
+  @visibleForTesting
+  Uri get archiveUri => Uri.parse('$_storageBaseUrl/flutter_infra/ios-usb-dependencies${cache.useUnsignedMacBinaries ? '/unsigned' : ''}/$name/$version/$name.zip');
 }
 
 // Many characters are problematic in filenames, especially on Windows.

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

diff --git a/packages/flutter_tools/lib/src/commands/precache.dart b/packages/flutter_tools/lib/src/commands/precache.dart
index d8ccd3a..0b145d6 100644
--- a/packages/flutter_tools/lib/src/commands/precache.dart
+++ b/packages/flutter_tools/lib/src/commands/precache.dart
@@ -44,6 +44,8 @@
         help: 'Precache artifacts required for any development platform.');
     argParser.addFlag('flutter_runner', negatable: true, defaultsTo: false,
         help: 'Precache the flutter runner artifacts.', hide: true);
+    argParser.addFlag('use-unsigned-mac-binaries', negatable: true, defaultsTo: false,
+        help: 'Precache the unsigned mac binaries when available.', hide: true);
   }
 
   @override
@@ -60,6 +62,9 @@
     if (argResults['all-platforms']) {
       cache.includeAllPlatforms = true;
     }
+    if (argResults['use-unsigned-mac-binaries']) {
+      cache.useUnsignedMacBinaries = true;
+    }
     final Set<DevelopmentArtifact> requiredArtifacts = <DevelopmentArtifact>{};
     for (DevelopmentArtifact artifact in DevelopmentArtifact.values) {
       // Don't include unstable artifacts on stable branches.

packages/flutter_tools/test/general.shard/cache_test.dart

diff --git a/packages/flutter_tools/test/general.shard/cache_test.dart b/packages/flutter_tools/test/general.shard/cache_test.dart
index a6a20a2..1c86af7 100644
--- a/packages/flutter_tools/test/general.shard/cache_test.dart
+++ b/packages/flutter_tools/test/general.shard/cache_test.dart
@@ -310,6 +310,32 @@
       ProcessManager: () => processManager,
     });
   });
+
+  group('Unsigned mac artifacts', () {
+    MockCache mockCache;
+
+    setUp(() {
+      mockCache = MockCache();
+    });
+
+    testUsingContext('use unsigned when specified', () async {
+      when(mockCache.useUnsignedMacBinaries).thenReturn(true);
+
+      final IosUsbArtifacts iosUsbArtifacts = IosUsbArtifacts('name', mockCache);
+      expect(iosUsbArtifacts.archiveUri.toString(), contains('/unsigned/'));
+    }, overrides: <Type, Generator>{
+      Cache: () => mockCache,
+    });
+
+    testUsingContext('not use unsigned when not specified', () async {
+      when(mockCache.useUnsignedMacBinaries).thenReturn(false);
+
+      final IosUsbArtifacts iosUsbArtifacts = IosUsbArtifacts('name', mockCache);
+      expect(iosUsbArtifacts.archiveUri.toString(), isNot(contains('/unsigned/')));
+    }, overrides: <Type, Generator>{
+      Cache: () => mockCache,
+    });
+  });
 }
 
 class FakeCachedArtifact extends EngineCachedArtifact {