Add incremental updates for multipage distillation.

components/dom_distiller/core/distiller_unittest.cc

Index: components/dom_distiller/core/distiller_unittest.cc
diff --git a/components/dom_distiller/core/distiller_unittest.cc b/components/dom_distiller/core/distiller_unittest.cc
index d3467c72aec481f1117c2b21b06cab57a27898c2..7eda8403f1dd856d07b3cd351537561d60ab7c4c 100644
--- a/components/dom_distiller/core/distiller_unittest.cc
+++ b/components/dom_distiller/core/distiller_unittest.cc
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#include <algorithm>
 #include <map>
 #include <string>
 #include <vector>
@@ -13,6 +14,7 @@
 #include "base/message_loop/message_loop.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/values.h"
+#include "components/dom_distiller/core/article_distillation_update.h"
 #include "components/dom_distiller/core/distiller.h"
 #include "components/dom_distiller/core/distiller_page.h"
 #include "components/dom_distiller/core/proto/distilled_article.pb.h"
@@ -58,6 +60,125 @@ namespace {
     return list.Pass();
   }
 
+  // Return the sequence in which Distiller will distill pages.
+  // Note: ignores any delays due to fetching images etc.
+  vector<int> get_pages_in_sequence(int start_page_num, int num_pages) {

[nyquist, 2014/03/03 23:00:12]

GetPagesInSequence

+    // Distiller prefers distilling past pages first. E.g. when distillation
+    // starts on page 2 then pages are distilled in the order: 2, 1, 0, 3, 4.
+    vector<int> page_nums;
+    for (int page = start_page_num; page >= 0; --page)
+      page_nums.push_back(page);
+    for (int page = start_page_num + 1; page < num_pages; ++page)
+      page_nums.push_back(page);
+    return page_nums;
+  }
+
+  struct MultipageDistillerData {
+   public:
+    MultipageDistillerData() {}
+    ~MultipageDistillerData() {}
+    vector<string> page_urls;
+    vector<string> content;
+    vector<vector<int> > image_ids;
+    // The Javascript values returned by mock distiller.
+    ScopedVector<base::Value> distilled_values;
+
+   private:
+    DISALLOW_COPY_AND_ASSIGN(MultipageDistillerData);
+  };
+
+  void VerifyIncrementalUpdatesMatch(
+      const MultipageDistillerData* distiller_data,
+      int num_pages_in_article,
+      const vector<dom_distiller::ArticleDistillationUpdate>&
+          incremental_updates,
+      int start_page_num) {
+    vector<int> page_seq =
+        get_pages_in_sequence(start_page_num, num_pages_in_article);
+    // Updates should contain a list of pages. Pages in a update should be in

[nyquist, 2014/03/03 23:00:12]

'an update'

[shashi, 2014/03/04 19:47:23]

Done.

+    // the correct ascending page order regardless of start_page_num.

[nyquist, 2014/03/03 23:00:12]

|start_page_num|

[shashi, 2014/03/04 19:47:23]

Done.

+    // E.g. if distillation starts at page 2 of a 3 page article, the updates
+    // will be [[2], [1, 2], [1, 2, 3]]. This example assumes that image fetches
+    // do not delay distillation of a page. There can be scenarios when image
+    // fetch delays distillation of a page (E.g. 1 is delayed due to image
+    // fetches so updates can be in this order [[2], [2,3], [1,2,3]].
+    for (size_t update_count = 0; update_count < incremental_updates.size();
+         ++update_count) {
+      const dom_distiller::ArticleDistillationUpdate& update =
+          incremental_updates[update_count];
+      EXPECT_EQ(update_count + 1, update.GetPagesSize());
+
+      vector<int> expected_page_nums_in_update(
+          page_seq.begin(), page_seq.begin() + update.GetPagesSize());
+      std::sort(expected_page_nums_in_update.begin(),
+                expected_page_nums_in_update.end());
+
+      // If we already got the first page then there is no previous page.
+      EXPECT_EQ((expected_page_nums_in_update[0] != 0), update.HasPrevPage());
+
+      // if we already got the last page then there is no next page.
+      EXPECT_EQ(
+          (*expected_page_nums_in_update.rbegin()) != num_pages_in_article - 1,
+          update.HasNextPage());
+      for (size_t j = 0; j < update.GetPagesSize(); ++j) {
+        int actual_page_num = expected_page_nums_in_update[j];
+        EXPECT_EQ(distiller_data->page_urls[actual_page_num],
+                  update.GetDistilledPage(j)->data.url());
+        EXPECT_EQ(distiller_data->content[actual_page_num],
+                  update.GetDistilledPage(j)->data.html());
+      }
+    }
+  }
+
+  scoped_ptr<MultipageDistillerData> CreateMultipageDistillerDataWithoutImages(
+      size_t pages_size) {
+    scoped_ptr<MultipageDistillerData> result(new MultipageDistillerData());
+    string url_prefix = "http://a.com/";
+    for (size_t page_num = 0; page_num < pages_size; ++page_num) {
+      result->page_urls.push_back(url_prefix + base::IntToString(page_num));
+      result->content.push_back("Content for page:" +
+                                base::IntToString(page_num));
+      result->image_ids.push_back(vector<int>());
+      string next_page_url = (page_num + 1 < pages_size)
+                                 ? url_prefix + base::IntToString(page_num + 1)
+                                 : "";
+      string prev_page_url =
+          (page_num > 0) ? result->page_urls[page_num - 1] : "";
+      scoped_ptr<base::ListValue> distilled_value =
+          CreateDistilledValueReturnedFromJS(kTitle,
+                                             result->content[page_num],
+                                             result->image_ids[page_num],
+                                             next_page_url,
+                                             prev_page_url);
+      result->distilled_values.push_back(distilled_value.release());
+    }
+    return result.Pass();
+  }
+
+  void VerifyArticleProtoMatchesMultipageData(
+      const dom_distiller::DistilledArticleProto* article_proto,
+      const MultipageDistillerData* distiller_data,
+      size_t pages_size) {
+    EXPECT_EQ(pages_size, static_cast<size_t>(article_proto->pages_size()));
+    EXPECT_EQ(kTitle, article_proto->title());
+    for (size_t page_num = 0; page_num < pages_size; ++page_num) {
+      const dom_distiller::DistilledPageProto& page =
+          article_proto->pages(page_num);
+      EXPECT_EQ(distiller_data->content[page_num], page.html());
+      EXPECT_EQ(distiller_data->page_urls[page_num], page.url());
+      EXPECT_EQ(distiller_data->image_ids[page_num].size(),
+                static_cast<size_t>(page.image_size()));
+      const vector<int>& image_ids_for_page =
+          distiller_data->image_ids[page_num];
+      for (size_t img_num = 0; img_num < image_ids_for_page.size(); ++img_num) {
+        EXPECT_EQ(kImageData[image_ids_for_page[img_num]],
+                  page.image(img_num).data());
+        EXPECT_EQ(GetImageName(page_num + 1, img_num),
+                  page.image(img_num).name());
+      }
+    }
+  }
+
 }  // namespace
 
 namespace dom_distiller {
@@ -85,7 +206,6 @@ class TestDistillerURLFetcher : public DistillerURLFetcher {
   std::map<string, string> responses_;
 };
 
-
 class TestDistillerURLFetcherFactory : public DistillerURLFetcherFactory {
  public:
   TestDistillerURLFetcherFactory() : DistillerURLFetcherFactory(NULL) {}
@@ -95,7 +215,6 @@ class TestDistillerURLFetcherFactory : public DistillerURLFetcherFactory {
   }
 };
 
-
 class MockDistillerPage : public DistillerPage {
  public:
   MOCK_METHOD0(InitImpl, void());
@@ -106,7 +225,6 @@ class MockDistillerPage : public DistillerPage {
       : DistillerPage(delegate) {}
 };
 
-
 class MockDistillerPageFactory : public DistillerPageFactory {
  public:
   MOCK_CONST_METHOD1(
@@ -122,13 +240,26 @@ class MockDistillerPageFactory : public DistillerPageFactory {
 class DistillerTest : public testing::Test {
  public:
   virtual ~DistillerTest() {}
-  void OnDistillPageDone(scoped_ptr<DistilledArticleProto> proto) {
+  void OnDistillArticleDone(scoped_ptr<DistilledArticleProto> proto) {
     article_proto_ = proto.Pass();
   }
 
+  void OnDistillArticleUpdate(const ArticleDistillationUpdate& article_update) {
+    in_sequence_updates_.push_back(article_update);
+  }
+
+  void DistillPage(const std::string& url) {
+    distiller_->DistillPage(GURL(url),
+                            base::Bind(&DistillerTest::OnDistillArticleDone,
+                                       base::Unretained(this)),
+                            base::Bind(&DistillerTest::OnDistillArticleUpdate,
+                                       base::Unretained(this)));
+  }
+
  protected:
   scoped_ptr<DistillerImpl> distiller_;
   scoped_ptr<DistilledArticleProto> article_proto_;
+  std::vector<ArticleDistillationUpdate> in_sequence_updates_;
   MockDistillerPageFactory page_factory_;
   TestDistillerURLFetcherFactory url_fetcher_factory_;
 };
@@ -149,29 +280,25 @@ ACTION_P2(CreateMockDistillerPage, list, kurl) {
   return distiller_page;
 }
 
-ACTION_P4(CreateMockDistillerPages, lists, kurls, num_pages, start_page_num) {
+ACTION_P3(CreateMockDistillerPages,
+          distiller_data,
+          pages_size,
+          start_page_num) {
   DistillerPage::Delegate* delegate = arg0;
   MockDistillerPage* distiller_page = new MockDistillerPage(delegate);
   EXPECT_CALL(*distiller_page, InitImpl());
   {
     testing::InSequence s;
-    // Distiller prefers distilling past pages first. E.g. when distillation
-    // starts on page 2 then pages are distilled in the order: 2, 1, 0, 3, 4.
-    vector<int> page_nums;
-    for (int page = start_page_num; page >= 0; --page)
-      page_nums.push_back(page);
-    for (int page = start_page_num + 1; page < num_pages; ++page)
-      page_nums.push_back(page);
-
-    for (size_t page_num = 0; page_num < page_nums.size(); ++page_num) {
+    vector<int> page_nums = get_pages_in_sequence(start_page_num, pages_size);
+    for (size_t page_num = 0; page_num < pages_size; ++page_num) {
       int page = page_nums[page_num];
-      GURL url = GURL(kurls[page]);
+      GURL url = GURL(distiller_data->page_urls[page]);
       EXPECT_CALL(*distiller_page, LoadURLImpl(url))
           .WillOnce(testing::InvokeWithoutArgs(distiller_page,
                                                &DistillerPage::OnLoadURLDone));
       EXPECT_CALL(*distiller_page, ExecuteJavaScriptImpl(_))
           .WillOnce(DistillerPageOnExecuteJavaScriptDone(
-              distiller_page, url, lists[page].get()));
+              distiller_page, url, distiller_data->distilled_values[page]));
     }
   }
   return distiller_page;
@@ -185,9 +312,7 @@ TEST_F(DistillerTest, DistillPage) {
       .WillOnce(CreateMockDistillerPage(list.get(), GURL(kURL)));
   distiller_.reset(new DistillerImpl(page_factory_, url_fetcher_factory_));
   distiller_->Init();
-  distiller_->DistillPage(
-      GURL(kURL),
-      base::Bind(&DistillerTest::OnDistillPageDone, base::Unretained(this)));
+  DistillPage(kURL);
   base::MessageLoop::current()->RunUntilIdle();
   EXPECT_EQ(kTitle, article_proto_->title());
   EXPECT_EQ(article_proto_->pages_size(), 1);
@@ -203,14 +328,11 @@ TEST_F(DistillerTest, DistillPageWithImages) {
   image_indices.push_back(1);
   scoped_ptr<base::ListValue> list =
       CreateDistilledValueReturnedFromJS(kTitle, kContent, image_indices, "");
-  EXPECT_CALL(page_factory_,
-              CreateDistillerPageMock(_)).WillOnce(
-                  CreateMockDistillerPage(list.get(), GURL(kURL)));
+  EXPECT_CALL(page_factory_, CreateDistillerPageMock(_))
+      .WillOnce(CreateMockDistillerPage(list.get(), GURL(kURL)));
   distiller_.reset(new DistillerImpl(page_factory_, url_fetcher_factory_));
   distiller_->Init();
-  distiller_->DistillPage(
-      GURL(kURL),
-      base::Bind(&DistillerTest::OnDistillPageDone, base::Unretained(this)));
+  DistillPage(kURL);
   base::MessageLoop::current()->RunUntilIdle();
   EXPECT_EQ(kTitle, article_proto_->title());
   EXPECT_EQ(article_proto_->pages_size(), 1);
@@ -226,59 +348,32 @@ TEST_F(DistillerTest, DistillPageWithImages) {
 
 TEST_F(DistillerTest, DistillMultiplePages) {
   base::MessageLoopForUI loop;
-  const int kNumPages = 8;
-  vector<int> image_indices[kNumPages];
-  string content[kNumPages];
-  string page_urls[kNumPages];
-  scoped_ptr<base::ListValue> list[kNumPages];
+  const size_t kNumPages = 8;
+  scoped_ptr<MultipageDistillerData> distiller_data =
+      CreateMultipageDistillerDataWithoutImages(kNumPages);
 
+  // Add images.
   int next_image_number = 0;
-
-  for (int page_num = 0; page_num < kNumPages; ++page_num) {
+  for (size_t page_num = 0; page_num < kNumPages; ++page_num) {
     // Each page has different number of images.
-    int tot_images = (page_num + kTotalImages) % (kTotalImages + 1);
-    for (int img_num = 0; img_num < tot_images; img_num++) {
-      image_indices[page_num].push_back(next_image_number);
+    size_t tot_images = (page_num + kTotalImages) % (kTotalImages + 1);
+    vector<int> image_indices;
+    for (size_t img_num = 0; img_num < tot_images; img_num++) {
+      image_indices.push_back(next_image_number);
       next_image_number = (next_image_number + 1) % kTotalImages;
     }
-
-    page_urls[page_num] = "http://a.com/" + base::IntToString(page_num);
-    content[page_num] = "Content for page:" + base::IntToString(page_num);
-  }
-  for (int i = 0; i < kNumPages; ++i) {
-    string next_page_url = "";
-    if (i + 1 < kNumPages)
-      next_page_url = page_urls[i + 1];
-
-    list[i] = CreateDistilledValueReturnedFromJS(
-        kTitle, content[i], image_indices[i], next_page_url);
+    distiller_data->image_ids.push_back(image_indices);
   }
 
   EXPECT_CALL(page_factory_, CreateDistillerPageMock(_))
-      .WillOnce(CreateMockDistillerPages(list, page_urls, kNumPages, 0));
+      .WillOnce(CreateMockDistillerPages(distiller_data.get(), kNumPages, 0));
 
   distiller_.reset(new DistillerImpl(page_factory_, url_fetcher_factory_));
   distiller_->Init();
-  distiller_->DistillPage(
-      GURL(page_urls[0]),
-      base::Bind(&DistillerTest::OnDistillPageDone, base::Unretained(this)));
+  DistillPage(distiller_data->page_urls[0]);
   base::MessageLoop::current()->RunUntilIdle();
-  EXPECT_EQ(kTitle, article_proto_->title());
-  EXPECT_EQ(article_proto_->pages_size(), kNumPages);
-  for (int page_num = 0; page_num < kNumPages; ++page_num) {
-    const DistilledPageProto& page = article_proto_->pages(page_num);
-    EXPECT_EQ(content[page_num], page.html());
-    EXPECT_EQ(page_urls[page_num], page.url());
-    EXPECT_EQ(image_indices[page_num].size(),
-              static_cast<size_t>(page.image_size()));
-    for (size_t img_num = 0; img_num < image_indices[page_num].size();
-         ++img_num) {
-      EXPECT_EQ(kImageData[image_indices[page_num][img_num]],
-                page.image(img_num).data());
-      EXPECT_EQ(GetImageName(page_num + 1, img_num),
-                page.image(img_num).name());
-    }
-  }
+  VerifyArticleProtoMatchesMultipageData(
+      article_proto_.get(), distiller_data.get(), kNumPages);
 }
 
 TEST_F(DistillerTest, DistillLinkLoop) {
@@ -291,84 +386,62 @@ TEST_F(DistillerTest, DistillLinkLoop) {
       .WillOnce(CreateMockDistillerPage(list.get(), GURL(kURL)));
   distiller_.reset(new DistillerImpl(page_factory_, url_fetcher_factory_));
   distiller_->Init();
-  distiller_->DistillPage(
-      GURL(kURL),
-      base::Bind(&DistillerTest::OnDistillPageDone, base::Unretained(this)));
+  DistillPage(kURL);
   base::MessageLoop::current()->RunUntilIdle();
   EXPECT_EQ(kTitle, article_proto_->title());
   EXPECT_EQ(article_proto_->pages_size(), 1);
 }
 
-TEST_F(DistillerTest, CheckMaxPageLimit) {
+TEST_F(DistillerTest, CheckMaxPageLimitExtraPage) {
   base::MessageLoopForUI loop;
   const size_t kMaxPagesInArticle = 10;
-  string page_urls[kMaxPagesInArticle];
-  scoped_ptr<base::ListValue> list[kMaxPagesInArticle];
+  scoped_ptr<MultipageDistillerData> distiller_data =
+      CreateMultipageDistillerDataWithoutImages(kMaxPagesInArticle);
 
   // Note: Next page url of the last page of article is set. So distiller will
   // try to do kMaxPagesInArticle + 1 calls if the max article limit does not
   // work.
-  string url_prefix = "http://a.com/";
-  for (size_t page_num = 0; page_num < kMaxPagesInArticle; ++page_num) {
-    page_urls[page_num] = url_prefix + base::IntToString(page_num + 1);
-    string content = "Content for page:" + base::IntToString(page_num);
-    string next_page_url = url_prefix + base::IntToString(page_num + 2);
-    list[page_num] = CreateDistilledValueReturnedFromJS(
-        kTitle, content, vector<int>(), next_page_url);
-  }
-
-  EXPECT_CALL(page_factory_, CreateDistillerPageMock(_))
-      .WillOnce(CreateMockDistillerPages(
-          list, page_urls, static_cast<int>(kMaxPagesInArticle), 0));
-
+  scoped_ptr<base::ListValue> last_page_data =
+      CreateDistilledValueReturnedFromJS(
+          kTitle,
+          distiller_data->content[kMaxPagesInArticle - 1],
+          vector<int>(),
+          "",
+          distiller_data->page_urls[kMaxPagesInArticle - 2]);
+
+  distiller_data->distilled_values.pop_back();
+  distiller_data->distilled_values.push_back(last_page_data.release());
+
+  EXPECT_CALL(page_factory_, CreateDistillerPageMock(_)).WillOnce(
+      CreateMockDistillerPages(distiller_data.get(), kMaxPagesInArticle, 0));
   distiller_.reset(new DistillerImpl(page_factory_, url_fetcher_factory_));
 
   distiller_->SetMaxNumPagesInArticle(kMaxPagesInArticle);
 
   distiller_->Init();
-  distiller_->DistillPage(
-      GURL(page_urls[0]),
-      base::Bind(&DistillerTest::OnDistillPageDone, base::Unretained(this)));
+  DistillPage(distiller_data->page_urls[0]);
   base::MessageLoop::current()->RunUntilIdle();
   EXPECT_EQ(kTitle, article_proto_->title());
   EXPECT_EQ(kMaxPagesInArticle,
             static_cast<size_t>(article_proto_->pages_size()));
+}
 
-  // Now check if distilling an article with exactly the page limit works by
-  // resetting the next page url of the last page of the article.
-  list[kMaxPagesInArticle - 1] =
-      CreateDistilledValueReturnedFromJS(kTitle, "Content", vector<int>(), "");
-  EXPECT_CALL(page_factory_, CreateDistillerPageMock(_))
-      .WillOnce(CreateMockDistillerPages(
-          list, page_urls, static_cast<int>(kMaxPagesInArticle), 0));
+TEST_F(DistillerTest, CheckMaxPageLimitExactLimit) {
+  base::MessageLoopForUI loop;
+  const size_t kMaxPagesInArticle = 10;
+  scoped_ptr<MultipageDistillerData> distiller_data =
+      CreateMultipageDistillerDataWithoutImages(kMaxPagesInArticle);
 
+  EXPECT_CALL(page_factory_, CreateDistillerPageMock(_)).WillOnce(
+      CreateMockDistillerPages(distiller_data.get(), kMaxPagesInArticle, 0));
   distiller_.reset(new DistillerImpl(page_factory_, url_fetcher_factory_));
-  distiller_->SetMaxNumPagesInArticle(kMaxPagesInArticle);
 
-  distiller_->Init();
-  distiller_->DistillPage(
-      GURL(page_urls[0]),
-      base::Bind(&DistillerTest::OnDistillPageDone, base::Unretained(this)));
-  base::MessageLoop::current()->RunUntilIdle();
-  EXPECT_EQ(kTitle, article_proto_->title());
-  EXPECT_EQ(kMaxPagesInArticle,
-            static_cast<size_t>(article_proto_->pages_size()));
-
-  // Now check if distilling an article with exactly the page limit works by
-  // resetting the next page url of the last page of the article.
-  list[kMaxPagesInArticle - 1] =
-      CreateDistilledValueReturnedFromJS(kTitle, "Content", vector<int>(), "");
-  EXPECT_CALL(page_factory_, CreateDistillerPageMock(_))
-      .WillOnce(CreateMockDistillerPages(
-          list, page_urls, static_cast<int>(kMaxPagesInArticle), 0));
-
-  distiller_.reset(new DistillerImpl(page_factory_, url_fetcher_factory_));
+  // Check if distilling an article with exactly the page limit works.
   distiller_->SetMaxNumPagesInArticle(kMaxPagesInArticle);
 
   distiller_->Init();
-  distiller_->DistillPage(
-      GURL(page_urls[0]),
-      base::Bind(&DistillerTest::OnDistillPageDone, base::Unretained(this)));
+
+  DistillPage(distiller_data->page_urls[0]);
   base::MessageLoop::current()->RunUntilIdle();
   EXPECT_EQ(kTitle, article_proto_->title());
   EXPECT_EQ(kMaxPagesInArticle,
@@ -383,9 +456,7 @@ TEST_F(DistillerTest, SinglePageDistillationFailure) {
       .WillOnce(CreateMockDistillerPage(nullValue.get(), GURL(kURL)));
   distiller_.reset(new DistillerImpl(page_factory_, url_fetcher_factory_));
   distiller_->Init();
-  distiller_->DistillPage(
-      GURL(kURL),
-      base::Bind(&DistillerTest::OnDistillPageDone, base::Unretained(this)));
+  DistillPage(kURL);
   base::MessageLoop::current()->RunUntilIdle();
   EXPECT_EQ("", article_proto_->title());
   EXPECT_EQ(0, article_proto_->pages_size());
@@ -393,83 +464,125 @@ TEST_F(DistillerTest, SinglePageDistillationFailure) {
 
 TEST_F(DistillerTest, MultiplePagesDistillationFailure) {
   base::MessageLoopForUI loop;
-  const int kNumPages = 8;
-  string content[kNumPages];
-  string page_urls[kNumPages];
-  scoped_ptr<base::Value> distilled_values[kNumPages];
-  // The page number of the failed page.
-  int failed_page_num = 3;
-  string url_prefix = "http://a.com/";
-  for (int page_num = 0; page_num < kNumPages; ++page_num) {
-    page_urls[page_num] = url_prefix + base::IntToString(page_num);
-    content[page_num] = "Content for page:" + base::IntToString(page_num);
-    string next_page_url = url_prefix + base::IntToString(page_num + 1);
-    if (page_num != failed_page_num) {
-      distilled_values[page_num] = CreateDistilledValueReturnedFromJS(
-          kTitle, content[page_num], vector<int>(), next_page_url);
-    } else {
-      distilled_values[page_num].reset(base::Value::CreateNullValue());
-    }
-  }
+  const size_t kNumPages = 8;
+  scoped_ptr<MultipageDistillerData> distiller_data =
+      CreateMultipageDistillerDataWithoutImages(kNumPages);
 
+  // The page number of the failed page.
+  size_t failed_page_num = 3;
+  // reset distilled data of the failed page.
+  distiller_data->distilled_values.erase(
+      distiller_data->distilled_values.begin() + failed_page_num);
+  distiller_data->distilled_values.insert(
+      distiller_data->distilled_values.begin() + failed_page_num,
+      base::Value::CreateNullValue());
   // Expect only calls till the failed page number.
+  EXPECT_CALL(page_factory_, CreateDistillerPageMock(_)).WillOnce(
+      CreateMockDistillerPages(distiller_data.get(), failed_page_num + 1, 0));
+
+  distiller_.reset(new DistillerImpl(page_factory_, url_fetcher_factory_));
+  distiller_->Init();
+  DistillPage(distiller_data->page_urls[0]);
+  base::MessageLoop::current()->RunUntilIdle();
+  EXPECT_EQ(kTitle, article_proto_->title());
+  VerifyArticleProtoMatchesMultipageData(
+      article_proto_.get(), distiller_data.get(), failed_page_num);
+}
+
+TEST_F(DistillerTest, DistillPreviousPage) {
+  base::MessageLoopForUI loop;
+  const size_t kNumPages = 8;
+
+  // The page number of the article on which distillation starts.
+  int start_page_num = 3;
+  scoped_ptr<MultipageDistillerData> distiller_data =
+      CreateMultipageDistillerDataWithoutImages(kNumPages);
+
+  EXPECT_CALL(page_factory_, CreateDistillerPageMock(_))
+      .WillOnce(CreateMockDistillerPages(
+          distiller_data.get(), kNumPages, start_page_num));
+
+  distiller_.reset(new DistillerImpl(page_factory_, url_fetcher_factory_));
+  distiller_->Init();
+  DistillPage(distiller_data->page_urls[start_page_num]);
+  base::MessageLoop::current()->RunUntilIdle();
+  VerifyArticleProtoMatchesMultipageData(
+      article_proto_.get(), distiller_data.get(), kNumPages);
+}
+
+TEST_F(DistillerTest, IncrementalUpdates) {
+  base::MessageLoopForUI loop;
+  const size_t kNumPages = 8;
+
+  // The page number of the article on which distillation starts.
+  int start_page_num = 3;
+  scoped_ptr<MultipageDistillerData> distiller_data =
+      CreateMultipageDistillerDataWithoutImages(kNumPages);
+
   EXPECT_CALL(page_factory_, CreateDistillerPageMock(_))
       .WillOnce(CreateMockDistillerPages(
-          distilled_values, page_urls, failed_page_num + 1, 0));
+          distiller_data.get(), kNumPages, start_page_num));
 
   distiller_.reset(new DistillerImpl(page_factory_, url_fetcher_factory_));
   distiller_->Init();
-  distiller_->DistillPage(
-      GURL(page_urls[0]),
-      base::Bind(&DistillerTest::OnDistillPageDone, base::Unretained(this)));
+  DistillPage(distiller_data->page_urls[start_page_num]);
   base::MessageLoop::current()->RunUntilIdle();
   EXPECT_EQ(kTitle, article_proto_->title());
-  EXPECT_EQ(article_proto_->pages_size(), failed_page_num);
-  for (int page_num = 0; page_num < failed_page_num; ++page_num) {
-    const DistilledPageProto& page = article_proto_->pages(page_num);
-    EXPECT_EQ(content[page_num], page.html());
-    EXPECT_EQ(page_urls[page_num], page.url());
-  }
+  EXPECT_EQ(kNumPages, static_cast<size_t>(article_proto_->pages_size()));
+  EXPECT_EQ(kNumPages, in_sequence_updates_.size());
+
+  VerifyIncrementalUpdatesMatch(
+      distiller_data.get(), kNumPages, in_sequence_updates_, start_page_num);
 }
 
-TEST_F(DistillerTest, DistillPreviousPage) {
+TEST_F(DistillerTest, IncrementalUpdatesDoNotDeleteFinalArticle) {
   base::MessageLoopForUI loop;
-  const int kNumPages = 8;
-  string content[kNumPages];
-  string page_urls[kNumPages];
-  scoped_ptr<base::Value> distilled_values[kNumPages];
+  const size_t kNumPages = 8;
+  int start_page_num = 3;
+  scoped_ptr<MultipageDistillerData> distiller_data =
+      CreateMultipageDistillerDataWithoutImages(kNumPages);
 
+  EXPECT_CALL(page_factory_, CreateDistillerPageMock(_))
+      .WillOnce(CreateMockDistillerPages(
+          distiller_data.get(), kNumPages, start_page_num));
+
+  distiller_.reset(new DistillerImpl(page_factory_, url_fetcher_factory_));
+  distiller_->Init();
+  DistillPage(distiller_data->page_urls[start_page_num]);
+  base::MessageLoop::current()->RunUntilIdle();
+  EXPECT_EQ(kNumPages, in_sequence_updates_.size());
+
+  in_sequence_updates_.clear();
+
+  // Should still be able to access article and pages.
+  VerifyArticleProtoMatchesMultipageData(
+      article_proto_.get(), distiller_data.get(), kNumPages);
+}
+
+TEST_F(DistillerTest, DeletingArticleDoesNotInterfereWithUpdates) {
+  base::MessageLoopForUI loop;
+  const size_t kNumPages = 8;
+  scoped_ptr<MultipageDistillerData> distiller_data =
+      CreateMultipageDistillerDataWithoutImages(kNumPages);
   // The page number of the article on which distillation starts.
-  int start_page_number = 3;
-  string url_prefix = "http://a.com/";
-  for (int page_no = 0; page_no < kNumPages; ++page_no) {
-    page_urls[page_no] = url_prefix + base::IntToString(page_no);
-    content[page_no] = "Content for page:" + base::IntToString(page_no);
-    string next_page_url = (page_no + 1 < kNumPages)
-                               ? url_prefix + base::IntToString(page_no + 1)
-                               : "";
-    string prev_page_url = (page_no > 0) ? page_urls[page_no - 1] : "";
-    distilled_values[page_no] = CreateDistilledValueReturnedFromJS(
-        kTitle, content[page_no], vector<int>(), next_page_url, prev_page_url);
-  }
+  int start_page_num = 3;
 
   EXPECT_CALL(page_factory_, CreateDistillerPageMock(_))
       .WillOnce(CreateMockDistillerPages(
-          distilled_values, page_urls, kNumPages, start_page_number));
+          distiller_data.get(), kNumPages, start_page_num));
 
   distiller_.reset(new DistillerImpl(page_factory_, url_fetcher_factory_));
   distiller_->Init();
-  distiller_->DistillPage(
-      GURL(page_urls[start_page_number]),
-      base::Bind(&DistillerTest::OnDistillPageDone, base::Unretained(this)));
+  DistillPage(distiller_data->page_urls[start_page_num]);
   base::MessageLoop::current()->RunUntilIdle();
+  EXPECT_EQ(kNumPages, in_sequence_updates_.size());
   EXPECT_EQ(kTitle, article_proto_->title());
-  EXPECT_EQ(kNumPages, article_proto_->pages_size());
-  for (int page_no = 0; page_no < kNumPages; ++page_no) {
-    const DistilledPageProto& page = article_proto_->pages(page_no);
-    EXPECT_EQ(content[page_no], page.html());
-    EXPECT_EQ(page_urls[page_no], page.url());
-  }
+  EXPECT_EQ(kNumPages, static_cast<size_t>(article_proto_->pages_size()));
+
+  // Delete the article.
+  article_proto_.reset();
+  VerifyIncrementalUpdatesMatch(
+      distiller_data.get(), kNumPages, in_sequence_updates_, start_page_num);
 }
 
 }  // namespace dom_distiller