Record Net.ProxyScriptFetcher.FirstByteDuration

This measures how long until the first byte is received for a PAC script. It's possible that we want to terminate fetching a PAC script if time-to-first-byte is longer than a specific cutoff point, rather than total time for the entire PAC script.

BUG=251682

Review URL: https://codereview.chromium.org/1302613003

Cr-Commit-Position: refs/heads/master@{#344819}

3 files changed, 27 insertions, 6 deletions

diff --git a/net/proxy/proxy_script_fetcher_impl.cc b/net/proxy/proxy_script_fetcher_impl.cc
index 6534150..8f728f7 100644
--- a/net/proxy/proxy_script_fetcher_impl.cc
+++ b/net/proxy/proxy_script_fetcher_impl.cc
@@ -135,7 +135,7 @@ int ProxyScriptFetcherImpl::Fetch(
   }
 
   DCHECK(fetch_start_time_.is_null());
-  fetch_start_time_ = base::Time::Now();
+  fetch_start_time_ = base::TimeTicks::Now();
 
   cur_request_ =
       url_request_context_->CreateRequest(url, DEFAULT_PRIORITY, this);
@@ -280,6 +280,11 @@ bool ProxyScriptFetcherImpl::ConsumeBytesRead(URLRequest* request,
     return false;
   }
 
+  if (bytes_read_so_far_.empty()) {
+    DCHECK(fetch_time_to_first_byte_.is_null());
+    fetch_time_to_first_byte_ = base::TimeTicks::Now();
+  }
+
   bytes_read_so_far_.append(buf_->data(), num_bytes);
   return true;
 }
@@ -288,8 +293,11 @@ void ProxyScriptFetcherImpl::FetchCompleted() {
   if (result_code_ == OK) {
     // Calculate duration of time for proxy script fetch to complete.
     DCHECK(!fetch_start_time_.is_null());
-    UMA_HISTOGRAM_TIMES("Net.ProxyScriptFetcher.SuccessDuration",
-                        base::Time::Now() - fetch_start_time_);
+    DCHECK(!fetch_time_to_first_byte_.is_null());
+    UMA_HISTOGRAM_MEDIUM_TIMES("Net.ProxyScriptFetcher.SuccessDuration",
+                               base::TimeTicks::Now() - fetch_start_time_);
+    UMA_HISTOGRAM_MEDIUM_TIMES("Net.ProxyScriptFetcher.FirstByteDuration",
+                               fetch_time_to_first_byte_ - fetch_start_time_);
 
     // The caller expects the response to be encoded as UTF16.
     std::string charset;
@@ -314,7 +322,8 @@ void ProxyScriptFetcherImpl::ResetCurRequestState() {
   callback_.Reset();
   result_code_ = OK;
   result_text_ = NULL;
-  fetch_start_time_ = base::Time();
+  fetch_start_time_ = base::TimeTicks();
+  fetch_time_to_first_byte_ = base::TimeTicks();
 }
 
 void ProxyScriptFetcherImpl::OnTimeout(int id) {
diff --git a/net/proxy/proxy_script_fetcher_impl.h b/net/proxy/proxy_script_fetcher_impl.h
index 85ad7a0..b02c9fc 100644
--- a/net/proxy/proxy_script_fetcher_impl.h
+++ b/net/proxy/proxy_script_fetcher_impl.h
@@ -117,7 +117,10 @@ class NET_EXPORT ProxyScriptFetcherImpl : public ProxyScriptFetcher,
   base::TimeDelta max_duration_;
 
   // The time that the fetch started.
-  base::Time fetch_start_time_;
+  base::TimeTicks fetch_start_time_;
+
+  // The time that the first byte was received.
+  base::TimeTicks fetch_time_to_first_byte_;
 
   // Factory for creating the time-out task. This takes care of revoking
   // outstanding tasks when |this| is deleted.
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index 4aefbff..cb3760f 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -22743,11 +22743,20 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <summary>The length of the URL that was passed into the PAC script.</summary>
 </histogram>
 
+<histogram name="Net.ProxyScriptFetcher.FirstByteDuration" units="milliseconds">
+  <owner>cbentzel@chromium.org</owner>
+  <summary>
+    The time taken from requesting a PAC script to receiving the first byte, on
+    successful fetches. This does not include time spent doing proxy
+    auto-discovery, or failed attempts at retrieving PAC  scripts.
+  </summary>
+</histogram>
+
 <histogram name="Net.ProxyScriptFetcher.SuccessDuration" units="milliseconds">
   <owner>cbentzel@chromium.org</owner>
   <summary>
     The time taken to successfully fetch a PAC script. This does not include
-    time spent doing proxy auto-discovery, or failed attempts at retrieiving PAC
+    time spent doing proxy auto-discovery, or failed attempts at retrieving PAC
     scripts.
   </summary>
 </histogram>