Add initial implementation of flutter assemble (#32816)

packages/flutter_tools/lib/src/artifacts.dart

diff --git a/packages/flutter_tools/lib/src/artifacts.dart b/packages/flutter_tools/lib/src/artifacts.dart
index 1c7c178..65a8b63 100644
--- a/packages/flutter_tools/lib/src/artifacts.dart
+++ b/packages/flutter_tools/lib/src/artifacts.dart
@@ -14,10 +14,13 @@
 import 'globals.dart';
 
 enum Artifact {
+  /// The tool which compiles a dart kernel file into native code.
   genSnapshot,
+  /// The flutter tester binary.
   flutterTester,
   snapshotDart,
   flutterFramework,
+  /// The framework directory of the macOS desktop.
   flutterMacOSFramework,
   vmSnapshotData,
   isolateSnapshotData,
@@ -25,12 +28,24 @@
   platformLibrariesJson,
   flutterPatchedSdkPath,
   frontendServerSnapshotForEngineDartSdk,
+  /// The root directory of the dartk SDK.
   engineDartSdkPath,
+  /// The dart binary used to execute any of the required snapshots.
   engineDartBinary,
+  /// The dart snapshot of the dart2js compiler.
   dart2jsSnapshot,
+  /// The dart snapshot of the dartdev compiler.
   dartdevcSnapshot,
+  /// The dart snpashot of the kernel worker compiler.
   kernelWorkerSnapshot,
+  /// The root of the web implementation of the dart SDK.
   flutterWebSdk,
+  /// The root of the Linux desktop sources.
+  linuxDesktopPath,
+  /// The root of the Windows desktop sources.
+  windowsDesktopPath,
+  /// The root of the sky_engine package
+  skyEnginePath,
 }
 
 String _artifactToFileName(Artifact artifact, [ TargetPlatform platform, BuildMode mode ]) {
@@ -47,6 +62,10 @@
     case Artifact.flutterFramework:
       return 'Flutter.framework';
     case Artifact.flutterMacOSFramework:
+      if (platform != TargetPlatform.darwin_x64)  {
+        throw Exception('${getNameForTargetPlatform(platform)} does not support'
+            ' macOS desktop development');
+      }
       return 'FlutterMacOS.framework';
     case Artifact.vmSnapshotData:
       return 'vm_isolate_snapshot.bin';
@@ -74,6 +93,20 @@
       return 'dartdevc.dart.snapshot';
     case Artifact.kernelWorkerSnapshot:
       return 'kernel_worker.dart.snapshot';
+    case Artifact.linuxDesktopPath:
+      if (platform != TargetPlatform.linux_x64)  {
+        throw Exception('${getNameForTargetPlatform(platform)} does not support'
+            ' Linux desktop development');
+      }
+      return '';
+    case Artifact.windowsDesktopPath:
+      if (platform != TargetPlatform.windows_x64)  {
+        throw Exception('${getNameForTargetPlatform(platform)} does not support'
+            ' Windows desktop development');
+      }
+      return '';
+    case Artifact.skyEnginePath:
+      return 'sky_engine';
   }
   assert(false, 'Invalid artifact $artifact.');
   return null;
@@ -209,9 +242,14 @@
       case Artifact.kernelWorkerSnapshot:
         return fs.path.join(dartSdkPath, 'bin', 'snapshots', _artifactToFileName(artifact));
       case Artifact.flutterMacOSFramework:
+      case Artifact.linuxDesktopPath:
+      case Artifact.windowsDesktopPath:
         final String engineArtifactsPath = cache.getArtifactDirectory('engine').path;
         final String platformDirName = getNameForTargetPlatform(platform);
         return fs.path.join(engineArtifactsPath, platformDirName, _artifactToFileName(artifact, platform, mode));
+      case Artifact.skyEnginePath:
+        final Directory dartPackageDirectory = cache.getCacheDir('pkg');
+        return fs.path.join(dartPackageDirectory.path,  _artifactToFileName(artifact));
       default:
         assert(false, 'Artifact $artifact not available for platform $platform.');
         return null;
@@ -302,6 +340,12 @@
         return fs.path.join(dartSdkPath, 'bin', 'snapshots', _artifactToFileName(artifact));
       case Artifact.kernelWorkerSnapshot:
         return fs.path.join(_hostEngineOutPath, 'dart-sdk', 'bin', 'snapshots', _artifactToFileName(artifact));
+      case Artifact.linuxDesktopPath:
+        return fs.path.join(_hostEngineOutPath, _artifactToFileName(artifact));
+      case Artifact.windowsDesktopPath:
+        return fs.path.join(_hostEngineOutPath, _artifactToFileName(artifact));
+      case Artifact.skyEnginePath:
+        return fs.path.join(_hostEngineOutPath, 'gen', 'dart-pkg', _artifactToFileName(artifact));
     }
     assert(false, 'Invalid artifact $artifact.');
     return null;