Add some basic UMA for proxy service.

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 6ab5e53c7de7317fa5ed83535e298fa1b9143cd8..7e6e2717c1a86ce28f48879cb0fabbc1896317f3 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -19862,6 +19862,41 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <summary>The length of the URL that was passed into the PAC script.</summary>
 </histogram>
 
+<histogram name="Net.ProxyService.GetProxyUsingScriptTime">
+  <owner>eroman@chromium.org</owner>
+  <summary>
+    The time taken to resolve a URL by forwarding the request to the proxy
+    resolver and executing the PAC script. This includes PAC script execution
+    and DNS queries, but does not include retries due to errors and changing
+    configurations.
+  </summary>
+</histogram>
+
+<histogram name="Net.ProxyService.ResolvedUsingScript">
+  <owner>eroman@chromium.org</owner>
+  <summary>
+    Whether proxy resolution occured by forwarding the request to the proxy
+    resolver and executing the PAC script.
+  </summary>
+</histogram>
+
+<histogram name="Net.ProxyService.ResolveProxyTime">
+  <owner>eroman@chromium.org</owner>
+  <summary>
+    The total time taken to resolve a URL. THis includes PAC script execution,
+    DNS queries, and retries.
+  </summary>
+</histogram>
+
+<histogram name="Net.ProxyService.ScriptTerminated">
+  <owner>eroman@chromium.org</owner>
+  <summary>
+    Whether a proxy resolution resulted in the PAC script terminating
+    unexpectedly. This happens when the resolver process crashes when using
+    out-of-process PAC.
+  </summary>
+</histogram>
+
 <histogram name="Net.PublicKeyPinFailureDomain" enum="PublicKeyPinFailedDomain">
   <owner>agl@chromium.org</owner>
   <summary>