cups_proxy/proxy_manager.cc: Always log rate limit exceeded warnings

If packets are rate limited by CUPS proxy, the print request will
probably fail. We want this information to always be logged so that we
can determine whether or not rate limiting is the cause of the print
failure by looking through the log.

Bug: 1157699
Change-Id: If1cb5689ca8f645a63ea93a0b4e368d83319e88e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2586756Reviewed-by: Sean Kau <skau@chromium.org>
Commit-Queue: Sean Kau <skau@chromium.org>
Cr-Commit-Position: refs/heads/master@{#836211}

chrome/services/cups_proxy/proxy_manager.cc

@@ -158,8 +158,8 @@ void ProxyManagerImpl::ProxyRequest(
       time - timestamp_.ReadBuffer(0) < base::TimeDelta::FromSeconds(1);
   timestamp_.SaveToBuffer(time);
   if (block_request) {
-    DVLOG(1) << "CupsPrintService Error: Rate limit (" << kRateLimit
-             << ") exceeded";
+    LOG(WARNING) << "CupsPrintService: Rate limit (" << kRateLimit
+                 << ") exceeded";
     std::move(cb).Run({}, {}, 429);  // HTTP_STATUS_TOO_MANY_REQUESTS
     return;
   }