[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

Review URL: https://chromiumcodereview.appspot.com/10910229

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@156327 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 13 insertions, 11 deletions

diff --git a/net/dns/dns_hosts.cc b/net/dns/dns_hosts.cc
index 668d202..66290b4 100644
--- a/net/dns/dns_hosts.cc
+++ b/net/dns/dns_hosts.cc
@@ -6,6 +6,7 @@
 
 #include "base/file_util.h"
 #include "base/logging.h"
+#include "base/metrics/histogram.h"
 #include "base/string_tokenizer.h"
 #include "base/string_util.h"
 
@@ -47,24 +48,25 @@ void ParseHosts(const std::string& contents, DnsHosts* dns_hosts) {
   }
 }
 
-// Reads the contents of the file at |path| into |str| if the total length is
-// less than |max_size|.
-static bool ReadFile(const FilePath& path, int64 max_size, std::string* str) {
-  int64 size;
-  if (!file_util::GetFileSize(path, &size) || size > max_size)
-    return false;
-  return file_util::ReadFileToString(path, str);
-}
-
 bool ParseHostsFile(const FilePath& path, DnsHosts* dns_hosts) {
   dns_hosts->clear();
   // Missing file indicates empty HOSTS.
   if (!file_util::PathExists(path))
     return true;
 
-  std::string contents;
+  int64 size;
+  if (!file_util::GetFileSize(path, &size))
+    return false;
+
+  UMA_HISTOGRAM_COUNTS("AsyncDNS.HostsSize", size);
+
+  // Reject HOSTS files larger than |kMaxHostsSize|.
   const int64 kMaxHostsSize = 1 << 16;
-  if (!ReadFile(path, kMaxHostsSize, &contents))
+  if (size > kMaxHostsSize)
+    return false;
+
+  std::string contents;
+  if (!file_util::ReadFileToString(path, &contents))
     return false;
 
   ParseHosts(contents, dns_hosts);