Even if some requests are send against cache.iridium.de still a lot of other requests are send against the original googles servers :

See part of squid log (logfile format combined)

::1 - - [01/Mar/2017:23:03:51 +0100] "CONNECT safebrowsing.google.com:443 HTTP/1.1" 200 61926 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Iridium/54.0 Safari/537.36 Chrome/54.0.2840.71" TCP_TUNNEL:HIER_DIRECT
::1 - - [01/Mar/2017:23:03:59 +0100] "CONNECT safebrowsing-cache.google.com:443 HTTP/1.1" 200 2494693 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Iridium/54.0 Safari/537.36 Chrome/54.0.2840.71" TCP_TUNNEL:HIER_DIRECT
::1 - - [01/Mar/2017:23:19:00 +0100] "CONNECT safebrowsing.google.com:443 HTTP/1.1" 200 42706 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Iridium/54.0 Safari/537.36 Chrome/54.0.2840.71" TCP_TUNNEL:HIER_DIRECT
::1 - - [01/Mar/2017:23:19:06 +0100] "CONNECT safebrowsing-cache.google.com:443 HTTP/1.1" 200 2277143 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Iridium/54.0 Safari/537.36 Chrome/54.0.2840.71" TCP_TUNNEL:HIER_DIRECT
::1 - - [01/Mar/2017:23:34:07 +0100] "CONNECT safebrowsing.google.com:443 HTTP/1.1" 200 45239 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Iridium/54.0 Safari/537.36 Chrome/54.0.2840.71" TCP_TUNNEL:HIER_DIRECT
::1 - - [01/Mar/2017:23:34:14 +0100] "CONNECT safebrowsing-cache.google.com:443 HTTP/1.1" 200 2039826 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Iridium/54.0 Safari/537.36 Chrome/54.0.2840.71" TCP_TUNNEL:HIER_DIRECT
## ::1 - - [01/Mar/2017:23:41:28 +0100] "CONNECT cache.iridiumbrowser.de:443 HTTP/1.1" 200 6086 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Iridium/54.0 Safari/537.36 Chrome/54.0.2840.71" TCP_TUNNEL:HIER_DIRECT
**
::1 - - [01/Mar/2017:23:41:28 +0100] "CONNECT cache.iridiumbrowser.de:443 HTTP/1.1" 200 6086 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Iridium/54.0 Safari/537.36 Chrome/54.0.2840.71" TCP_TUNNEL:HIER_DIRECT
::1 - - [01/Mar/2017:23:49:15 +0100] "CONNECT safebrowsing.google.com:443 HTTP/1.1" 200 28452 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Iridium/54.0 Safari/537.36 Chrome/54.0.2840.71" TCP_TUNNEL:HIER_DIRECT
**
::1 - - [01/Mar/2017:23:49:19 +0100] "CONNECT safebrowsing-cache.google.com:443 HTTP/1.1" 200 1477656 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Iridium/54.0 Safari/537.36 Chrome/54.0.2840.71" TCP_TUNNEL:HIER_DIRECT
::1 - - [02/Mar/2017:00:04:20 +0100] "CONNECT safebrowsing.google.com:443 HTTP/1.1" 200 7618 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Iridium/54.0 Safari/537.36 Chrome/54.0.2840.71" TCP_TUNNEL:HIER_DIRECT
::1 - - [02/Mar/2017:00:04:23 +0100] "CONNECT safebrowsing-cache.google.com:443 HTTP/1.1" 200 1029863 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Iridium/54.0 Safari/537.36 Chrome/54.0.2840.71" TCP_TUNNEL:HIER_DIRECT
::1 - - [02/Mar/2017:00:19:24 +0100] "CONNECT safebrowsing.google.com:443 HTTP/1.1" 200 4949 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Iridium/54.0 Safari/537.36 Chrome/54.0.2840.71" TCP_TUNNEL:HIER_DIRECT
::1 - - [02/Mar/2017:00:19:25 +0100] "CONNECT safebrowsing-cache.google.com:443 HTTP/1.1" 200 690110 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Iridium/54.0 Safari/537.36 Chrome/54.0.2840.71" TCP_TUNNEL:HIER_DIRECT
::1 - - [02/Mar/2017:00:34:26 +0100] "CONNECT safebrowsing.google.com:443 HTTP/1.1" 200 1856 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Iridium/54.0 Safari/537.36 Chrome/54.0.2840.71" TCP_TUNNEL:HIER_DIRECT
::1 - - [02/Mar/2017:00:34:27 +0100] "CONNECT safebrowsing-cache.google.com:443 HTTP/1.1" 200 4420 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Iridium/54.0 Safari/537.36 Chrome/54.0.2840.71" TCP_TUNNEL:HIER_DIRECT
::1 - - [02/Mar/2017:00:41:28 +0100] "CONNECT cache.iridiumbrowser.de:443 HTTP/1.1" 200 6086 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Iridium/54.0 Safari/537.36 Chrome/54.0.2840.71" TCP_TUNNEL:HIER_DIRECT
::1 - - [02/Mar/2017:00:41:28 +0100] "CONNECT cache.iridiumbrowser.de:443 HTTP/1.1" 200 6086 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Iridium/54.0 Safari/537.36 Chrome/54.0.2840.71" TCP_TUNNEL:HIER_DIRECT
::1 - - [02/Mar/2017:00:49:28 +0100] "CONNECT safebrowsing.google.com:443 HTTP/1.1" 200 6144 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Iridium/54.0 Safari/537.36 Chrome/54.0.2840.71" TCP_TUNNEL:HIER_DIRECT
::1 - - [02/Mar/2017:00:49:28 +0100] "CONNECT safebrowsing-cache.google.com:443 HTTP/1.1" 200 8413 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Iridium/54.0 Safari/537.36 Chrome/54.0.2840.71" TCP_TUNNEL:HIER_DIRECT
::1 - - [02/Mar/2017:01:04:29 +0100] "CONNECT safebrowsing.google.com:443 HTTP/1.1" 200 1399 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Iridium/54.0 Safari/537.36 Chrome/54.0.2840.71" TCP_TUNNEL:HIER_DIRECT
::1 - - [02/Mar/2017:01:04:30 +0100] "CONNECT safebrowsing-cache.google.com:443 HTTP/1.1" 200 2262 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Iridium/54.0 Safari/537.36 Chrome/54.0.2840.71" TCP_TUNNEL:HIER_DIRECT
::1 - - [02/Mar/2017:01:19:30 +0100] "CONNECT safebrowsing.google.com:443 HTTP/1.1" 200 1388 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Iridium/54.0 Safari/537.36 Chrome/54.0.2840.71" TCP_TUNNEL:HIER_DIRECT
::1 - - [02/Mar/2017:01:19:31 +0100] "CONNECT safebrowsing-cache.google.com:443 HTTP/1.1" 200 1389 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Iridium/54.0 Safari/537.36 Chrome/54.0.2840.71" TCP_TUNNEL:HIER_DIRECT