URL Formatter: Add StripSubdomain method that preserves eTLD + 1.

components/url_formatter/url_formatter_unittest.cc

Index: components/url_formatter/url_formatter_unittest.cc
diff --git a/components/url_formatter/url_formatter_unittest.cc b/components/url_formatter/url_formatter_unittest.cc
index 544f55080a4c6eb940f53e55082d9db2e0346762..746f21e1c138db46cf76d3b6a0d2f3eae37b1b43 100644
--- a/components/url_formatter/url_formatter_unittest.cc
+++ b/components/url_formatter/url_formatter_unittest.cc
@@ -1223,6 +1223,38 @@ TEST(UrlFormatterTest, FormatUrlWithOffsets) {
                        net::UnescapeRule::NORMAL, omit_all_offsets);
 }
 
+TEST(UrlFormatterTest, StripSubdomains) {
+  struct TestCase {
+    std::string expected;
+    std::string input_host;
+    StripSubdomainTypes subdomains_to_strip;
+  } cases[] = {
+      // Test successful strippings of subdomains.
+      {"google.com", "www.google.com", kStripWWW},
+      {"google.com", "m.google.com", kStripM},
+      {"google.com", "www.google.com", kStripWWW | kStripM},
+      {"google.com", "m.google.com", kStripWWW | kStripM},
+
+      // Only strip one least-significant subdomain.

[Peter Kasting, 2017/06/17 02:46:55]

Yeah, this seems not-what-we-want to me.

[tommycli, 2017/06/19 23:03:08]

Done.

+      {"m.google.com", "www.m.google.com", kStripWWW | kStripM},
+      {"www.google.com", "m.www.google.com", kStripWWW | kStripM},
+

[Peter Kasting, 2017/06/17 02:46:55]

There are no tests for "strip www from m.foo.com" and "strip m from
www.foo.com".

[tommycli, 2017/06/19 23:03:08]

Done.

+      // Leave eTLD+1s alone.
+      {"google.com", "google.com", kStripWWW},
+      {"www.com", "www.com", kStripWWW | kStripM},
+      {"m.com", "m.com", kStripWWW | kStripM},
+      {"mail.google.com", "mail.google.com", kStripWWW | kStripM},
+  };
+
+  for (size_t i = 0; i < arraysize(cases); ++i) {

[Peter Kasting, 2017/06/17 02:46:55]

Nit: Use range-based for instead

[tommycli, 2017/06/19 23:03:08]

Done.

+    EXPECT_EQ(cases[i].expected, url_formatter::StripSubdomains(
+                                     GURL("http://" + cases[i].input_host),
+                                     cases[i].subdomains_to_strip))
+        << "  input_host = " << cases[i].input_host << std::endl
+        << "  subdomains_to_strip = " << cases[i].subdomains_to_strip;
+  }
+}
+
 }  // namespace
 
 }  // namespace url_formatter