[ VM / CLI ] Run DartDev isolate from snapshot when possible

This change tries to run from dartdev.dart.snapshot and falls back to
running from dartdev.dill if incompatible VM flags are provided.

Fixes https://github.com/dart-lang/sdk/issues/43969

Performance results:

dart test.dart (no CLI isolate): 0.167s
dart run test (from snapshot):   0.208s
dart run test (from kernel):     0.326s

TEST=pkg/dartdev/test/load_from_dill_test.dart

Change-Id: I3195886b86676580ef2a0221f0284328964ef061
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/178300
Commit-Queue: Ben Konyi <bkonyi@google.com>
Reviewed-by: Siva Annamalai <asiva@google.com>

utils/dartdev/BUILD.gn

@@ -12,7 +12,10 @@ dartdev_files = exec_script("../../tools/list_dart_files.py",
                             "list lines")
 
 group("dartdev") {
-  public_deps = [ ":copy_dartdev_kernel" ]
+  public_deps = [
+    ":copy_dartdev_kernel",
+    ":copy_dartdev_snapshot",
+  ]
 }
 
 copy("copy_dartdev_kernel") {
@@ -30,3 +33,18 @@ application_snapshot("generate_dartdev_kernel") {
   inputs = dartdev_files
   output = "$root_gen_dir/dartdev.dill"
 }
+
+copy("copy_dartdev_snapshot") {
+  visibility = [ ":dartdev" ]
+  public_deps = [ ":generate_dartdev_snapshot" ]
+  sources = [ "$root_gen_dir/dartdev.dart.snapshot" ]
+  outputs = [ "$root_out_dir/dartdev.dart.snapshot" ]
+}
+
+application_snapshot("generate_dartdev_snapshot") {
+  main_dart = "../../pkg/dartdev/bin/dartdev.dart"
+  training_args = [ "--help" ]
+  deps = [ "../dds:dds" ]
+  inputs = dartdev_files
+  output = "$root_gen_dir/dartdev.dart.snapshot"
+}