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

chrome/browser/android/offline_pages/prerendering_loader.cc

Index: chrome/browser/android/offline_pages/prerendering_loader.cc
diff --git a/chrome/browser/android/offline_pages/prerendering_loader.cc b/chrome/browser/android/offline_pages/prerendering_loader.cc
index bbc1fe0851ac8f1d9753ce70fbdbde02b3ff795a..5ce6fb638b4bc41041cf12a9f318f8a698c9348a 100644
--- a/chrome/browser/android/offline_pages/prerendering_loader.cc
+++ b/chrome/browser/android/offline_pages/prerendering_loader.cc
@@ -58,7 +58,7 @@ bool PrerenderingLoader::LoadPage(const GURL& url,
       new SnapshotController(base::ThreadTaskRunnerHandle::Get(), this));
   callback_ = callback;
   session_contents_.swap(new_web_contents);
-  state_ = State::PENDING;
+  state_ = State::LOADING;
   return true;
 }
 
@@ -88,12 +88,6 @@ void PrerenderingLoader::SetAdapterForTesting(
   adapter_ = std::move(prerender_adapter);
 }
 
-void PrerenderingLoader::OnPrerenderStart() {
-  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
-  DCHECK(state_ == State::PENDING);
-  state_ = State::LOADING;
-}
-
 void PrerenderingLoader::OnPrerenderStopLoading() {
   DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
   DCHECK(!IsIdle());