[fetch keepalive] Loosen the limit on the size of URL and headers

Based on UMA data we increase the threshold to 512kb.

Bug: 1018050
Change-Id: Ic4ca9b3d8a959610c5e187d0eefdc0ee02fe785a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1885853Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Commit-Queue: Yutaka Hirano <yhirano@chromium.org>
Cr-Commit-Position: refs/heads/master@{#710231}

services/network/url_loader_factory.h

@@ -63,7 +63,7 @@ class URLLoaderFactory : public mojom::URLLoaderFactory {
 
   static constexpr int kMaxKeepaliveConnections = 2048;
   static constexpr int kMaxKeepaliveConnectionsPerProcess = 256;
-  static constexpr int kMaxTotalKeepaliveRequestSize = 256 * 1024;
+  static constexpr int kMaxTotalKeepaliveRequestSize = 512 * 1024;
 
  private:
   // The NetworkContext that indirectly owns |this|.