[Explore Sites] Fixing SQL query to gather icons for category tiles.

Previously, the SQL query included site icons that were NULL or empty,
resulting in category tiles often having less than 4 site icons present.
This fix skips the empty icons, and grabs the next non-empty ones.

Change-Id: I314c78f1797769e598640d06162811e1672c2449
Reviewed-on: https://chromium-review.googlesource.com/c/1279155Reviewed-by: Peter Williamson <petewil@chromium.org>
Commit-Queue: Jonathan Freed <freedjm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#599347}

chrome/browser/android/explore_sites/get_images_task.cc

@@ -16,7 +16,8 @@ namespace {
 const char kSelectCategoryImagesSql[] = R"(SELECT favicon
 FROM sites
 LEFT JOIN site_blacklist ON (sites.url = site_blacklist.url)
-WHERE category_id = ? AND NOT removed AND site_blacklist.url IS NULL
+WHERE category_id = ? AND LENGTH(favicon) > 0 AND NOT removed
+AND site_blacklist.url IS NULL
 LIMIT ?;)";
 
 const char kSelectSiteImageSql[] =

chrome/browser/android/explore_sites/get_images_task_unittest.cc

@@ -175,4 +175,25 @@ VALUES
   EXPECT_EQ(4U, last_result.size());
 }
 
+TEST_F(ExploreSitesGetImagesTaskTest, SkipMissingFavicons) {
+  PopulateTestingCatalog();
+  ExecuteSync(base::BindLambdaForTesting([&](sql::Database* db) {
+    sql::Statement insert(db->GetUniqueStatement(R"(
+INSERT INTO sites
+(site_id, url, category_id, title, favicon)
+VALUES
+(5, "https://www.example.com/5", 3, "example_5", NULL),
+(6, "https://www.example.com/6", 3, "example_6", ""),
+(7, "https://www.example.com/7", 3, "example_7", "bytes7");
+)"));
+    return insert.Run();
+  }));
+  GetImagesTask task(store(), 3, 3, StoreResult());
+  RunTask(&task);
+
+  EXPECT_EQ(3U, last_result.size());
+  std::vector<uint8_t>& result3 = *last_result[2];
+  EXPECT_EQ("bytes7", std::string(result3.begin(), result3.end()));
+}
+
 }  // namespace explore_sites