Add getTarget method to CompilerCommandLine

pkg/front_end/lib/src/fasta/compiler_command_line.dart

Index: pkg/front_end/lib/src/fasta/compiler_command_line.dart
diff --git a/pkg/front_end/lib/src/fasta/compiler_command_line.dart b/pkg/front_end/lib/src/fasta/compiler_command_line.dart
index 1c415a1229dba2d5ac6d45065fdf05d965a0bb7b..90a720d40e2d3c89c8b69fc414da620966988673 100644
--- a/pkg/front_end/lib/src/fasta/compiler_command_line.dart
+++ b/pkg/front_end/lib/src/fasta/compiler_command_line.dart
@@ -10,6 +10,9 @@ import 'command_line.dart' show CommandLine, argumentError;
 
 import 'compiler_context.dart' show CompilerContext;
 
+import 'package:kernel/target/targets.dart' as backend_targets
+    show Target, getTarget, TargetFlags;
+
 const Map<String, dynamic> optionSpecification = const <String, dynamic>{
   "--compile-sdk": Uri,
   "--fatal": ",",
@@ -23,6 +26,7 @@ const Map<String, dynamic> optionSpecification = const <String, dynamic>{
 
 class CompilerCommandLine extends CommandLine {
   final String programName;
+  backend_targets.Target cachedTarget;
 
   CompilerCommandLine(String programName, List<String> arguments)
       : programName = programName,
@@ -94,6 +98,14 @@ class CompilerCommandLine extends CommandLine {
     return options["-t"] ?? options["--target"] ?? "vm_fasta";
   }
 
+  backend_targets.Target getTarget() {

[ahe, 2017/06/08 14:49:37]

Change this to:

backend_targets.Target get target {

[Dmitry Stefantsov, 2017/06/09 08:24:40]

Done.

+    if (cachedTarget != null) {
+      return cachedTarget;
+    }
+    return cachedTarget = backend_targets.getTarget(

[ahe, 2017/06/08 14:49:37]

Use ??=

[Dmitry Stefantsov, 2017/06/09 08:24:40]

Thanks for the suggestion! It looks way better than if-return-than-return.

Also, now that we use eager caching during parameters validation, we don't need
this method body. But I'll keep the trick for when I need to lazily cache
things.

+        target, new backend_targets.TargetFlags(strongMode: strongMode));
+  }
+
   static dynamic withGlobalOptions(String programName, List<String> arguments,
       dynamic f(CompilerContext context)) {
     return CompilerContext.withGlobalOptions(