[sync] Add regression test for TabContentsSyncedTabDelegate crash

chrome/browser/ui/sync/tab_contents_synced_tab_delegate_unittest.cc

+// Copyright 2017 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.
+
+#include "chrome/browser/ui/sync/tab_contents_synced_tab_delegate.cc"
+
+#include "chrome/test/base/chrome_render_view_host_test_harness.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace {
+
+class TabContentsSyncedTabDelegateTest
+    : public ChromeRenderViewHostTestHarness {
+ public:
+  TabContentsSyncedTabDelegateTest() : ChromeRenderViewHostTestHarness() {}
+  ~TabContentsSyncedTabDelegateTest() override {}
+
+  void SetUp() override {
+    content::RenderViewHostTestHarness::SetUp();
+
+    NavigateAndCommit(GURL("about:blank"));
+    TabContentsSyncedTabDelegate::CreateForWebContents(web_contents());
+  }
+};
+
+TEST_F(TabContentsSyncedTabDelegateTest, InvalidEntryIndexReturnsDefault) {
+  std::unique_ptr<content::WebContents> web_contents(CreateTestWebContents());
+
+  TabContentsSyncedTabDelegate::CreateForWebContents(web_contents.get());
+
+  TabContentsSyncedTabDelegate* delegate =
+      TabContentsSyncedTabDelegate::FromWebContents(web_contents.get());
+
+  // -1 and 2 are invalid indices because there's only one navigation
+  // recorded(the initial one to "about:blank")
+  EXPECT_EQ(delegate->GetFaviconURLAtIndex(-1), GURL());
+  EXPECT_EQ(delegate->GetFaviconURLAtIndex(2), GURL());
+
+  EXPECT_TRUE(
+      PageTransitionCoreTypeIs(delegate->GetTransitionAtIndex(-1),
+                               ui::PageTransition::PAGE_TRANSITION_LINK));
+  EXPECT_TRUE(
+      PageTransitionCoreTypeIs(delegate->GetTransitionAtIndex(2),
+                               ui::PageTransition::PAGE_TRANSITION_LINK));
+}
+
+}  // namespace