[net/dns] Collect histogram on HOSTS file size.

[net/dns] Collect histogram on HOSTS file size.

4% of attempts to parse the HOSTS file fail because reading the file fails.
This is likely because files above 65kB are rejected. This CL installs the AsyncDNS.HostsSize
histogram to measure the observed size of HOSTS file on each call to ParseHostsFile.

BUG=137914
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=156327

[szym, 2012-09-12 16:42:35]

http://codereview.chromium.org/10910229/diff/1/net/dns/dns_hosts.cc
File net/dns/dns_hosts.cc (left):

http://codereview.chromium.org/10910229/diff/1/net/dns/dns_hosts.cc#oldcode52
net/dns/dns_hosts.cc:52: static bool ReadFile(const FilePath& path, int64
max_size, std::string* str) {
I removed this function because it doesn't seem to be that helpful.

[mmenke, 2012-09-12 16:46:48]

LGTM

[commit-bot: I haz the power, 2012-09-12 16:47:34]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/szym@chromium.org/10910229/1