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

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

Index: pkg/front_end/lib/src/fasta/kernel/kernel_shadow_ast.dart
diff --git a/pkg/front_end/lib/src/fasta/kernel/kernel_shadow_ast.dart b/pkg/front_end/lib/src/fasta/kernel/kernel_shadow_ast.dart
index 71f2b30b67e10b0059b217923d1396d2fcd81623..4ffa9b98af78b469cf19e30ffa76049341deac22 100644
--- a/pkg/front_end/lib/src/fasta/kernel/kernel_shadow_ast.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/kernel_shadow_ast.dart
@@ -1535,8 +1535,11 @@ class KernelRethrow extends Rethrow implements KernelExpression {
   @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;
   }
 }
 
@@ -1824,8 +1827,11 @@ class KernelThrow extends Throw implements KernelExpression {
   @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;
   }
 }