Implement subcomponent factory validation using the new binding graph model.

Extract the ComponentNode implementation into a class in dagger.internal.codegen with some nonpublic properties.

Add the ability to report an error for subcomponent factory methods.

Delete the now-empty BindingGraphValidator.

RELNOTES=n/a

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=201379680
diff --git a/java/dagger/internal/codegen/ComponentNodeImpl.java b/java/dagger/internal/codegen/ComponentNodeImpl.java
new file mode 100644
index 0000000..7b624aa
--- /dev/null
+++ b/java/dagger/internal/codegen/ComponentNodeImpl.java
@@ -0,0 +1,50 @@
+/*
+ * Copyright (C) 2018 The Dagger Authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package dagger.internal.codegen;
+
+import com.google.auto.value.AutoValue;
+import com.google.common.collect.ImmutableSet;
+import dagger.model.BindingGraph.ComponentNode;
+import dagger.model.ComponentPath;
+import dagger.model.DependencyRequest;
+import dagger.model.Scope;
+
+/** An implementation of {@link ComponentNode} that also exposes the {@link ComponentDescriptor}. */
+@AutoValue
+abstract class ComponentNodeImpl implements ComponentNode {
+  static ComponentNode create(
+      ComponentPath componentPath, ComponentDescriptor componentDescriptor) {
+    return new AutoValue_ComponentNodeImpl(componentPath, componentDescriptor);
+  }
+
+  @Override
+  public ImmutableSet<DependencyRequest> entryPoints() {
+    return componentDescriptor().entryPoints();
+  }
+
+  @Override
+  public ImmutableSet<Scope> scopes() {
+    return componentDescriptor().scopes();
+  }
+
+  abstract ComponentDescriptor componentDescriptor();
+
+  @Override
+  public final String toString() {
+    return componentPath().toString();
+  }
+}