Create an option to disable type inference and type promotion.

pkg/kernel/lib/target/targets.dart

Index: pkg/kernel/lib/target/targets.dart
diff --git a/pkg/kernel/lib/target/targets.dart b/pkg/kernel/lib/target/targets.dart
index 7389dc073975ac9726a1db5356a3e626a9a70199..c47c117fe972d1c61487e542d1d93fa44f648396 100644
--- a/pkg/kernel/lib/target/targets.dart
+++ b/pkg/kernel/lib/target/targets.dart
@@ -69,6 +69,13 @@ abstract class Target {
 
   bool get strongMode;
 
+  /// A derived class may change this to `true` to disable type inference and
+  /// type promotion phases of analysis.
+  ///
+  /// This is intended for profiling, to ensure that type inference and type
+  /// promotion do not slow down compilation too much.
+  bool get disableTypeInference => false;
+
   /// If true, the SDK should be loaded in strong mode.
   bool get strongModeSdk => strongMode;