Support type variables on redirecting factory constructors.

sdk/lib/_internal/compiler/implementation/ssa/builder.dart

Index: sdk/lib/_internal/compiler/implementation/ssa/builder.dart
diff --git a/sdk/lib/_internal/compiler/implementation/ssa/builder.dart b/sdk/lib/_internal/compiler/implementation/ssa/builder.dart
index b9ee92552b1812f06ac4140d5a009f24df7d49d7..94afd380b162337cd19044853ea8bbae153444f1 100644
--- a/sdk/lib/_internal/compiler/implementation/ssa/builder.dart
+++ b/sdk/lib/_internal/compiler/implementation/ssa/builder.dart
@@ -3378,6 +3378,7 @@ class SsaBuilder extends ResolvedVisitor implements Visitor {
     }
     FunctionElement functionElement = constructor;
     constructor = functionElement.redirectionTarget;
+
     final bool isSymbolConstructor =
         functionElement == compiler.symbolConstructor;
 
@@ -3390,6 +3391,23 @@ class SsaBuilder extends ResolvedVisitor implements Visitor {
                        message: 'Constructor Symbol.validated is missing'));
     }
 
+    bool isRedirected = functionElement.isRedirection;
+    DartType expectedType = type;
+    if (isRedirected) {
+      FunctionExpression functionNode = functionElement.parseNode(compiler);
+      if (functionNode.isRedirectingFactory) {
+        // Lookup the type used in the redirection.
+        Return redirectionNode = functionNode.body;
+        TreeElements treeElements =
+            compiler.enqueuer.resolution.getCachedElements(
+                functionElement.declaration);
+        ClassElement targetClass = functionElement.getEnclosingClass();
+        type = treeElements.getType(redirectionNode)
+            .subst(type.typeArguments, targetClass.typeVariables);
+      }
+      functionElement = functionElement.redirectionTarget;
+    }
+
     var inputs = <HInstruction>[];
     // TODO(5347): Try to avoid the need for calling [implementation] before
     // calling [addStaticSendArgumentsToList].
@@ -3434,6 +3452,15 @@ class SsaBuilder extends ResolvedVisitor implements Visitor {
     if (isListConstructor && backend.needsRti(compiler.listClass)) {
       handleListConstructor(type, send, newInstance);
     }
+
+    // Finally, if we called a redirecting factory constructor, check the type.
+    if (isRedirected) {
+      HInstruction checked = potentiallyCheckType(newInstance, expectedType);
+      if (checked != newInstance) {
+        pop();
+        stack.add(checked);
+      }
+    }
   }
 
   visitStaticSend(Send node) {