Revert of [Prerender] Restore request priorities when swapped in

chrome/browser/loader/chrome_resource_dispatcher_host_delegate.cc

Index: chrome/browser/loader/chrome_resource_dispatcher_host_delegate.cc
diff --git a/chrome/browser/loader/chrome_resource_dispatcher_host_delegate.cc b/chrome/browser/loader/chrome_resource_dispatcher_host_delegate.cc
index cc36f63584bf41e131932889a297f929981c2f81..ef5d5c416c517d104df1545a7a32ef83e320887a 100644
--- a/chrome/browser/loader/chrome_resource_dispatcher_host_delegate.cc
+++ b/chrome/browser/loader/chrome_resource_dispatcher_host_delegate.cc
@@ -443,6 +443,27 @@
     safe_browsing_->OnResourceRequest(request);
 
   const ResourceRequestInfo* info = ResourceRequestInfo::ForRequest(request);
+
+// The lowering of request priority causes issues with scheduling, since
+// content::ResourceScheduler uses it to delay and throttle requests. This is
+// disabled only on Android, as the prerenders are not likely to compete with
+// page loads there.
+// See https://crbug.com/652746 for details.
+// TODO(lizeb,droger): Fix the issue on all platforms.
+#if !defined(OS_ANDROID)
+  bool is_prerendering =
+      info->GetVisibilityState() == blink::kWebPageVisibilityStatePrerender;
+  if (is_prerendering) {
+    // Requests with the IGNORE_LIMITS flag set (i.e., sync XHRs)
+    // should remain at MAXIMUM_PRIORITY.
+    if (request->load_flags() & net::LOAD_IGNORE_LIMITS) {
+      DCHECK_EQ(request->priority(), net::MAXIMUM_PRIORITY);
+    } else {
+      request->SetPriority(net::IDLE);
+    }
+  }
+#endif  // OS_ANDROID
+
   ProfileIOData* io_data = ProfileIOData::FromResourceContext(
       resource_context);