Fix an issue that PrerenderLoader::OnPrerenderStart() never gets called.

chrome/browser/android/offline_pages/prerendering_loader_unittest.cc

Index: chrome/browser/android/offline_pages/prerendering_loader_unittest.cc
diff --git a/chrome/browser/android/offline_pages/prerendering_loader_unittest.cc b/chrome/browser/android/offline_pages/prerendering_loader_unittest.cc
index c558fbd3351907f5b9651cd67072ea5a2c8e3f38..eb0bf2bc15da74dbbc0ec01053420f60ebaebb56 100644
--- a/chrome/browser/android/offline_pages/prerendering_loader_unittest.cc
+++ b/chrome/browser/android/offline_pages/prerendering_loader_unittest.cc
@@ -218,7 +218,6 @@ TEST_F(PrerenderingLoaderTest, LoadPageLoadSucceededFromPrerenderStopLoading) {
       gurl,
       base::Bind(&PrerenderingLoaderTest::OnLoadDone, base::Unretained(this))));
 
-  test_adapter()->GetObserver()->OnPrerenderStart();
   PumpLoop();
   EXPECT_FALSE(loader()->IsIdle());
   EXPECT_FALSE(loader()->IsLoaded());