Add support for multipage distillation.

components/dom_distiller/core/proto/distilled_article.proto

Index: components/dom_distiller/core/proto/distilled_article.proto
diff --git a/components/dom_distiller/core/proto/distilled_article.proto b/components/dom_distiller/core/proto/distilled_article.proto
new file mode 100644
index 0000000000000000000000000000000000000000..54284bf162661e55f2c1a52b4866b6b50ffd1f7a
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+++ b/components/dom_distiller/core/proto/distilled_article.proto
@@ -0,0 +1,21 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+//
+// Distilled article content.
+
+syntax = "proto2";
+
+option optimize_for = LITE_RUNTIME;
+
+package dom_distiller;
+
+import "distilled_page.proto";
+
+message DistilledArticleProto {
+  // A title for the article.
+  optional string title = 1;
+
+  // The distilled pages in the article.
+  repeated DistilledPageProto pages = 2;
+}