Add a browsertest suite for net predictor

chrome/browser/net/predictor.h

Index: chrome/browser/net/predictor.h
diff --git a/chrome/browser/net/predictor.h b/chrome/browser/net/predictor.h
index 53ea6323ca8a610e9bbcc57faba79fa4666ee3c4..20af1749dddb726df8e44da0df2c17c80ba3e3e1 100644
--- a/chrome/browser/net/predictor.h
+++ b/chrome/browser/net/predictor.h
@@ -75,7 +75,9 @@ class PredictorObserver {
   virtual void OnPreconnectUrl(const GURL& original_url,
                                const GURL& first_party_for_cookies,
                                UrlInfo::ResolutionMotivation motivation,
-                               int count) = 0;
+                               int count) {}
+  virtual void OnLearnFromNavigation(const GURL& referring_url,
+                                     const GURL& target_url) {}
 };
 
 // Predictor is constructed during Profile construction (on the UI thread),
@@ -307,6 +309,10 @@ class Predictor {
     return predictor_enabled_;
   }
 
+  // Used only for testing.
+  void set_preconnect_enabled(bool preconnect_enabled) {

[mmenke, 2016/04/15 15:44:02]

set_preconnect_enabled_for_test

There's a clang check that _for_test / ForTest methods aren't called in
production, I believe.

[Charlie Harrison, 2016/04/20 12:36:42]

Done.

+    preconnect_enabled_ = preconnect_enabled;
+  }

[mmenke, 2016/04/15 15:44:02]

This doesn't seem threadsafe - this is accessed on both the IO and UI threads.

Unfortunately, the test fixture adds a command line switch to disable
preconnects (They break our really bad spawned test server).  I don't suppose we
can just remove that argument in SetUpCommandLine (Or whatever the test fixture
method is called)

[Charlie Harrison, 2016/04/20 12:36:42]

Hmmm. I can try that in another CL to see if anything breaks. We can always
selectively add the command line for breaking tests.

I'll leave this as is for now with the expectation that I'll find a better
solution later.

What would you think about adding another flag to override this one?

[mmenke, 2016/04/22 16:29:24]

We can't really selectively add the flag - every single test that uses the
embedded test server for a single navigation/resource will run into this.
I think adding another flag is a worse solution.

 
  private:
   FRIEND_TEST_ALL_PREFIXES(PredictorTest, BenefitLookupTest);
@@ -564,7 +570,7 @@ class Predictor {
   // Are we currently using preconnection, rather than just DNS resolution, for
   // subresources and omni-box search URLs.
   // This is false if and only if disabled by a command line switch.
-  const bool preconnect_enabled_;
+  bool preconnect_enabled_;
 
   // Most recent suggestion from Omnibox provided via AnticipateOmniboxUrl().
   std::string last_omnibox_host_;