Infer the types of initializing formals from the corresponding fields.

pkg/front_end/lib/src/fasta/kernel/kernel_formal_parameter_builder.dart

Index: pkg/front_end/lib/src/fasta/kernel/kernel_formal_parameter_builder.dart
diff --git a/pkg/front_end/lib/src/fasta/kernel/kernel_formal_parameter_builder.dart b/pkg/front_end/lib/src/fasta/kernel/kernel_formal_parameter_builder.dart
index d1ffc333984083d1802b3ab91d374438b48d8738..fc014eb7748add4aaa5d9ba3a62a75c4159ed2bb 100644
--- a/pkg/front_end/lib/src/fasta/kernel/kernel_formal_parameter_builder.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/kernel_formal_parameter_builder.dart
@@ -12,9 +12,11 @@ import 'kernel_builder.dart'
         FormalParameterBuilder,
         KernelLibraryBuilder,
         KernelTypeBuilder,
-        LibraryBuilder,
         MetadataBuilder;
 
+import 'package:front_end/src/fasta/source/source_library_builder.dart'
+    show SourceLibraryBuilder;
+
 class KernelFormalParameterBuilder
     extends FormalParameterBuilder<KernelTypeBuilder> {
   KernelVariableDeclaration declaration;
@@ -33,9 +35,16 @@ class KernelFormalParameterBuilder
 
   KernelVariableDeclaration get target => declaration;
 
-  KernelVariableDeclaration build(LibraryBuilder library) {
-    return declaration ??= new KernelVariableDeclaration(name, 0,
-        type: type?.build(library), isFinal: isFinal, isConst: isConst)
-      ..fileOffset = charOffset;
+  KernelVariableDeclaration build(SourceLibraryBuilder library) {
+    if (declaration == null) {
+      declaration = new KernelVariableDeclaration(name, 0,
+          type: type?.build(library), isFinal: isFinal, isConst: isConst)
+        ..fileOffset = charOffset;
+      if (type == null && hasThis) {
+        library.loader.typeInferenceEngine
+            .recordInitializingFormal(declaration);
+      }
+    }
+    return declaration;
   }
 }