Extract KernelCompiler class (#16937)

Wraps the compile function in a class injected via the global context,
which makes it easier to mock in unit tests -- specifically tests for
AOT snapshotting, which already require pretty significant amounts of
mock inputs.

packages/flutter_tools/lib/src/bundle.dart

@@ -106,7 +106,7 @@ Future<void> build({
     String kernelBinaryFilename;
     if (needBuild) {
       ensureDirectoryExists(applicationKernelFilePath);
-      final CompilerOutput compilerOutput = await compile(
+      final CompilerOutput compilerOutput = await kernelCompiler.compile(
         sdkRoot: artifacts.getArtifactPath(Artifact.flutterPatchedSdkPath),
         incrementalCompilerByteStorePath: fs.path.absolute(getIncrementalCompilerByteStoreDirectory()),
         mainPath: fs.file(mainPath).absolute.path,

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

@@ -366,7 +366,7 @@ Future<String> _buildAotSnapshot(
   }
 
   if (previewDart2) {
-    final CompilerOutput compilerOutput = await compile(
+    final CompilerOutput compilerOutput = await kernelCompiler.compile(
       sdkRoot: artifacts.getArtifactPath(Artifact.flutterPatchedSdkPath),
       mainPath: mainPath,
       outputFilePath: kApplicationKernelPath,

packages/flutter_tools/lib/src/compile.dart

@@ -9,10 +9,13 @@ import 'package:usage/uuid/uuid.dart';
 
 import 'artifacts.dart';
 import 'base/common.dart';
+import 'base/context.dart';
 import 'base/io.dart';
 import 'base/process_manager.dart';
 import 'globals.dart';
 
+KernelCompiler get kernelCompiler => context[KernelCompiler];
+
 typedef void CompilerMessageConsumer(String message);
 
 class CompilerOutput {
@@ -59,7 +62,10 @@ class _StdoutHandler {
   }
 }
 
-Future<CompilerOutput> compile(
+class KernelCompiler {
+  const KernelCompiler();
+
+  Future<CompilerOutput> compile(
     {String sdkRoot,
     String mainPath,
     String outputFilePath,
@@ -147,6 +153,7 @@ Future<CompilerOutput> compile(
       .listen(stdoutHandler.handler);
     final int exitCode = await server.exitCode;
     return exitCode == 0 ? stdoutHandler.compilerOutput.future : null;
+  }
 }
 
 /// Wrapper around incremental frontend server compiler, that communicates with

packages/flutter_tools/lib/src/context_runner.dart

@@ -22,6 +22,7 @@ import 'base/platform.dart';
 import 'base/port_scanner.dart';
 import 'base/utils.dart';
 import 'cache.dart';
+import 'compile.dart';
 import 'devfs.dart';
 import 'device.dart';
 import 'doctor.dart';
@@ -63,6 +64,7 @@ Future<T> runInContext<T>(
       IMobileDevice: () => const IMobileDevice(),
       IOSSimulatorUtils: () => new IOSSimulatorUtils(),
       IOSWorkflow: () => const IOSWorkflow(),
+      KernelCompiler: () => const KernelCompiler(),
       Logger: () => platform.isWindows ? new WindowsStdoutLogger() : new StdoutLogger(),
       OperatingSystemUtils: () => new OperatingSystemUtils(),
       PortScanner: () => const HostPortScanner(),

packages/flutter_tools/test/compile_test.dart

@@ -46,7 +46,7 @@ void main() {
               'result abc\nline1\nline2\nabc /path/to/main.dart.dill 0'
             ))
           ));
-      final CompilerOutput output = await compile(sdkRoot: '/path/to/sdkroot',
+      final CompilerOutput output = await kernelCompiler.compile(sdkRoot: '/path/to/sdkroot',
         mainPath: '/path/to/main.dart'
       );
       expect(mockFrontendServerStdIn.getAndClear(), isEmpty);
@@ -66,7 +66,7 @@ void main() {
             ))
           ));
 
-      final CompilerOutput output = await compile(sdkRoot: '/path/to/sdkroot',
+      final CompilerOutput output = await kernelCompiler.compile(sdkRoot: '/path/to/sdkroot',
         mainPath: '/path/to/main.dart'
       );
       expect(mockFrontendServerStdIn.getAndClear(), isEmpty);
@@ -88,7 +88,7 @@ void main() {
           ))
       ));
 
-      final CompilerOutput output = await compile(sdkRoot: '/path/to/sdkroot',
+      final CompilerOutput output = await kernelCompiler.compile(sdkRoot: '/path/to/sdkroot',
           mainPath: '/path/to/main.dart'
       );
       expect(mockFrontendServerStdIn.getAndClear(), isEmpty);