Add a cap of six in-flight requests per host to the ResourceScheduler

net/base/priority_queue.h

Index: net/base/priority_queue.h
diff --git a/net/base/priority_queue.h b/net/base/priority_queue.h
index 7b7d97c0e8e31764d737c59239338cd4a3c17d99..ab4be3ef1f29b8d3990122dc2fcdf9151a2f3a7e 100644
--- a/net/base/priority_queue.h
+++ b/net/base/priority_queue.h
@@ -264,6 +264,31 @@ class PriorityQueue : public base::NonThreadSafe {
     size_ = 0u;
   }
 
+  // This can be used to iterate through the composite container, in
+  // highest-to-lowest, first-inserted-to-last order.
+  Pointer NextHighest(const Pointer& previous) {
+    Priority priority = previous.priority_;
+    typename Pointer::ListIterator list_entry = previous.iterator_;
+
+    if (list_entry != lists_[priority].end()) {
+      ++list_entry;
+    }
+
+    while (priority < lists_.size()) {
+      if (list_entry == lists_[priority].end()) {
+        if (priority == 0) {
+          break;
+        }
+        priority--;
+        list_entry = lists_[priority].begin();
+      } else {
+        return Pointer(priority, list_entry);
+      }
+    }
+
+    return Pointer();
+  }
+
   // Returns the number of priorities the queue supports.
   size_t num_priorities() const {
     DCHECK(CalledOnValidThread());