Add a histogram (Net.PacResultForStrippedUrl) that estimates how often PAC scripts depend on the UR…

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index 60140b3367e41a614910052a1d7bdff63781a7fb..9057bb98e6168836735be94189222f50cfa1396a 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -26072,6 +26072,17 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Net.PacResultForStrippedUrl" enum="PacResultForStrippedUrl">
+  <owner>eroman@chromium.org</owner>
+  <summary>
+    Estimates the impact of PAC script results when the URL path and parameters
+    are elided, by running the PAC script a second time with a fixed path.
+
+    This is only measured for https:// and wss:// URL schemes in order to gather
+    data for crbug.com/593759.
+  </summary>
+</histogram>
+
 <histogram name="Net.Ping_ResponseStartedTime" units="ms">
   <obsolete>
     Deprecated 4/16/2014. No longer tracked.
@@ -76131,6 +76142,21 @@ To add a new entry, add it with any value and run test to compute valid value.
   <int value="4" label="Index"/>
 </enum>
 
+<enum name="PacResultForStrippedUrl" type="int">
+  <summary>
+    Result for PAC script experiment as defined in
+    net/proxy/proxy_resolver_v8_tracing.h
+  </summary>
+  <int value="0" label="SKIPPED_FALLBACK_BLOCKING_DNS"/>
+  <int value="1" label="SUCCESS"/>
+  <int value="2" label="SUCCESS_DIFFERENT_ALERTS"/>
+  <int value="3" label="SUCCESS_DIFFERENT_NUM_DNS"/>
+  <int value="4" label="FAIL_ABANDONED"/>
+  <int value="5" label="FAIL_FALLBACK_BLOCKING_DNS"/>
+  <int value="6" label="FAIL_ERROR"/>
+  <int value="7" label="FAIL_DIFFERENT_PROXY_LIST"/>
+</enum>
+
 <enum name="PageLoadEvent" type="int">
   <obsolete>
     Deprecated in favor of {Committed|Provisional|InternalError}LoadEvent