Fix a predictor browsertest for the PreconnectMore experiment

chrome/browser/net/predictor_browsertest.cc

Index: chrome/browser/net/predictor_browsertest.cc
diff --git a/chrome/browser/net/predictor_browsertest.cc b/chrome/browser/net/predictor_browsertest.cc
index 2afa4e96721d0872d3d05e109b80b7527c452498..0d18ab8ecc5e2ebf2abe62110c4eeb0db73b4b41 100644
--- a/chrome/browser/net/predictor_browsertest.cc
+++ b/chrome/browser/net/predictor_browsertest.cc
@@ -464,6 +464,8 @@ class PredictorBrowserTest : public InProcessBrowserTest {
         switches::kEnableExperimentalWebPlatformFeatures);
     command_line->AppendSwitchASCII(
         switches::kEnableBlinkFeatures, kBlinkPreconnectFeature);
+    command_line->AppendSwitchASCII(switches::kEnableFeatures,
+                                    "PreconnectMore");
   }
 
   void SetUpOnMainThread() override {
@@ -594,10 +596,13 @@ class PredictorBrowserTest : public InProcessBrowserTest {
     DCHECK_CURRENTLY_ON(BrowserThread::UI);
     observer_.reset(
         new CrossSitePredictorObserver(source_host, cross_site_host));
-    BrowserThread::PostTask(
+    base::RunLoop run_loop;

[mmenke, 2016/05/16 19:10:07]

These shouldn't be needed - anything that does any network activity on the IO
thread triggered after this point will necessarily happen after this event.  The
only concern would be if we tore down the test fixture before the task runs. 
Since we always wait on some IO thread task, shouldn't be a problem there.  So
this part of the CL is fine, but I don't think it fixes anything.

[Charlie Harrison, 2016/05/16 19:13:39]

Ack. Thanks for the clarification. I'll keep it for test simplicity (readers
don't have to know that implementation detail).

+    BrowserThread::PostTaskAndReply(
         BrowserThread::IO, FROM_HERE,
         base::Bind(&PredictorBrowserTest::InstallPredictorObserverOnIOThread,
-                   base::Unretained(this), base::Unretained(predictor())));
+                   base::Unretained(this), base::Unretained(predictor())),
+        run_loop.QuitClosure());
+    run_loop.Run();
   }
 
   void InstallPredictorObserverOnIOThread(