cups_proxy: Increase rate limit

Increase the rate limit to prevent pita tast tests from flaking

Unlike cupsCopyDestInfo(), cupsDoRequest() does not appear to retry
requests when the server is busy.

If the tests still flake, this limit may have to be increased again.

Bug: none
Test: tast run -buildbundle pita <DUT> printer.*

Change-Id: Idbd0f485cf47e059e9bd80a5b53e338887ba7d88
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2470302Reviewed-by: Sean Kau <skau@chromium.org>
Commit-Queue: Pranav Batra <batrapranav@chromium.org>
Auto-Submit: Pranav Batra <batrapranav@chromium.org>
Cr-Commit-Position: refs/heads/master@{#818725}

chrome/services/cups_proxy/proxy_manager.h

@@ -32,7 +32,7 @@ class SocketManager;
 class ProxyManager : public mojom::CupsProxier {
  public:
   // Request rate limit per second.
-  static constexpr int kRateLimit = 10;
+  static constexpr int kRateLimit = 20;
 
   // Factory function.
   static std::unique_ptr<ProxyManager> Create(