Prevent making real DNS lookups by chrome tests.

chrome/test/unit/chrome_test_suite.h

Index: chrome/test/unit/chrome_test_suite.h
diff --git a/chrome/test/unit/chrome_test_suite.h b/chrome/test/unit/chrome_test_suite.h
index 8dcdbf68a06e60cf0b8b78ad06b64737c9913cda..1d7947f64f967a7f15f71a6a2fbd248ce8950f46 100644
--- a/chrome/test/unit/chrome_test_suite.h
+++ b/chrome/test/unit/chrome_test_suite.h
@@ -13,6 +13,7 @@
 #include "base/mac_util.h"
 #endif
 #include "base/path_service.h"
+#include "base/ref_counted.h"
 #include "base/scoped_nsautorelease_pool.h"
 #include "base/test_suite.h"
 #include "chrome/app/scoped_ole_initializer.h"
@@ -21,6 +22,30 @@
 #include "chrome/common/chrome_switches.h"
 #include "chrome/common/resource_bundle.h"
 #include "chrome/test/testing_browser_process.h"
+#include "net/base/host_resolver_unittest.h"
+
+// In many cases it may be not obvious that a test makes a real DNS lookup.
+// We generally don't want to rely on external DNS servers for our tests,
+// so this mapper catches external queries.
+class WarningHostMapper : public net::HostMapper {
+ public:
+  virtual std::string Map(const std::string& host) {
+    const char* kLocalHostNames[] = {"localhost", "127.0.0.1"};
+    bool local = false;
+    for (size_t i = 0; i < arraysize(kLocalHostNames); i++)
+      if (host == kLocalHostNames[i]) {
+        local = true;
+        break;
+      }
+
+    // Make the test fail so it's harder to ignore.
+    // If you really need to make real DNS query, use net::RuleBasedHostMapper
+    // and its AllowDirectLookup method.
+    EXPECT_TRUE(local) << "Making external DNS lookup of " << host;
+
+    return MapUsingPrevious(host);
+  }
+};
 
 class ChromeTestSuite : public TestSuite {
 public:
@@ -34,6 +59,9 @@ protected:
 
     TestSuite::Initialize();
 
+    host_mapper_ = new WarningHostMapper();
+    scoped_host_mapper_.Init(host_mapper_.get());
+
     chrome::RegisterPathProvider();
     g_browser_process = new TestingBrowserProcess;
 
@@ -90,6 +118,8 @@ protected:
 
   StatsTable* stats_table_;
   ScopedOleInitializer ole_initializer_;
+  scoped_refptr<WarningHostMapper> host_mapper_;
+  net::ScopedHostMapper scoped_host_mapper_;
 };
 
 #endif // CHROME_TEST_UNIT_CHROME_TEST_SUITE_H_