Add/fix/cleanup type inference for throw and rethrow.

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

 // Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /// This file declares a "shadow hierarchy" of concrete classes which extend
 /// the kernel class hierarchy, adding methods and fields needed by the
 /// BodyBuilder.
 ///
 /// Instances of these classes may be created using the factory methods in
 /// `ast_factory.dart`.
@@ skipping 1517 matching lines @@
 /// Shadow object for [Rethrow].
 class KernelRethrow extends Rethrow implements KernelExpression {
   @override
   void _collectDependencies(KernelDependencyCollector collector) {
     // No inference dependencies.
   }
 
   @override
   DartType _inferExpression(
       KernelTypeInferrer inferrer, DartType typeContext, bool typeNeeded) {
-    // TODO(scheglov): implement.
-    return typeNeeded ? const DynamicType() : null;
+    typeNeeded =
+        inferrer.listener.rethrowEnter(this, typeContext) || typeNeeded;
+    var inferredType = typeNeeded ? const BottomType() : null;
+    inferrer.listener.rethrowExit(this, inferredType);
+    return inferredType;
   }
 }
 
 /// Concrete shadow object representing a return statement in kernel form.
 class KernelReturnStatement extends ReturnStatement implements KernelStatement {
   KernelReturnStatement([Expression expression]) : super(expression);
 
   @override
   void _inferStatement(KernelTypeInferrer inferrer) {
     inferrer.listener.returnStatementEnter(this);
@@ skipping 267 matching lines @@
   KernelThrow(Expression expression) : super(expression);
 
   @override
   void _collectDependencies(KernelDependencyCollector collector) {
     // No inference dependencies.
   }
 
   @override
   DartType _inferExpression(
       KernelTypeInferrer inferrer, DartType typeContext, bool typeNeeded) {
+    typeNeeded = inferrer.listener.throwEnter(this, typeContext) || typeNeeded;
     inferrer.inferExpression(expression, null, false);
-    return typeNeeded ? const BottomType() : null;
+    var inferredType = typeNeeded ? const BottomType() : null;
+    inferrer.listener.throwExit(this, inferredType);
+    return inferredType;
   }
 }
 
 /// Concrete implementation of [TypeInferenceEngine] specialized to work with
 /// kernel objects.
 class KernelTypeInferenceEngine extends TypeInferenceEngineImpl {
   KernelTypeInferenceEngine(Instrumentation instrumentation, bool strongMode)
       : super(instrumentation, strongMode);
 
   @override
@@ skipping 397 matching lines @@
   }
 
   transformChildren(v) {
     return internalError("Internal error: Unsupported operation.");
   }
 
   visitChildren(v) {
     return internalError("Internal error: Unsupported operation.");
   }
 }