[ABANDONED] [WIP] Schedule async revalidations after other requests.

content/browser/loader/resource_scheduler.cc

Index: content/browser/loader/resource_scheduler.cc
diff --git a/content/browser/loader/resource_scheduler.cc b/content/browser/loader/resource_scheduler.cc
index 7bc6c0458b86648b22e88ed16bd5cfceea8c52e6..69ec83d29357784f27da5f58a1bbd68d92477c7c 100644
--- a/content/browser/loader/resource_scheduler.cc
+++ b/content/browser/loader/resource_scheduler.cc
@@ -167,10 +167,13 @@ class ResourceScheduler::ScheduledResourceRequest
         request_(request),
         ready_(false),
         deferred_(false),
+        is_async_revalidation_(false),
         classification_(NORMAL_REQUEST),
         scheduler_(scheduler),
         priority_(priority),
         fifo_ordering_(0) {
+    is_async_revalidation_ =
+        ResourceRequestInfo::ForRequest(request)->IsAsyncRevalidation();
   }
 
   ~ScheduledResourceRequest() override { scheduler_->RemoveRequest(this); }
@@ -226,6 +229,7 @@ class ResourceScheduler::ScheduledResourceRequest
   void set_classification(RequestClassification classification) {
     classification_ = classification;
   }
+  bool is_async_revalidation() const { return is_async_revalidation_; }
 
  private:
   // ResourceMessageDelegate interface:
@@ -256,6 +260,7 @@ class ResourceScheduler::ScheduledResourceRequest
   net::URLRequest* request_;
   bool ready_;
   bool deferred_;
+  bool is_async_revalidation_;
   RequestClassification classification_;
   ResourceScheduler* scheduler_;
   RequestPriorityParams priority_;
@@ -268,6 +273,10 @@ class ResourceScheduler::ScheduledResourceRequest
 bool ResourceScheduler::ScheduledResourceSorter::operator()(
     const ScheduledResourceRequest* a,
     const ScheduledResourceRequest* b) const {
+  // Want all other requests to be ordered before async revalidations.
+  if (a->is_async_revalidation() != b->is_async_revalidation())
+    return b->is_async_revalidation();
+
   // Want the set to be ordered first by decreasing priority, then by
   // decreasing intra_priority.
   // ie. with (priority, intra_priority)
@@ -689,6 +698,10 @@ class ResourceScheduler::Client {
   //     UNTHROTTLED Client, and then return to the COALESCED state.
   //   * When an active Client makes a request, they are THROTTLED until the
   //     active Client finishes loading.
+  //
+  // 6. Async revalidations
+  //   * Async revalidations come after all other requests, and are never loaded
+  //     until the document has a body.
   ShouldStartReqResult ShouldStartRequest(
       ScheduledResourceRequest* request) const {
     const net::URLRequest& url_request = *request->url_request();
@@ -706,6 +719,12 @@ class ResourceScheduler::Client {
       return START_REQUEST;
     }
 
+    if (request->is_async_revalidation() && !has_body_) {
+      // Because async revalidations are sorted last, all following requests
+      // will also be async revalidations.
+      return DO_NOT_START_REQUEST_AND_STOP_SEARCHING;
+    }
+
     if (throttle_state_ == COALESCED) {
       return DO_NOT_START_REQUEST_AND_STOP_SEARCHING;
     }