Add UMAs for checking header values against RFC 7230 in //net

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 5f7a4025b7e4caa8608a8bfcef699e4fab7effb6..63034fb1849ebe06decb55018a5e7aba79c56cee 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -24245,6 +24245,15 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Net.HttpRequestContainsInvalidHeaderValuesInRFC7230"
+    enum="Boolean">
+  <owner>hiroshige@chromium.org</owner>
+  <summary>
+    Whether a request contains invalid request header values in RFC 7230. This
+    is counted once for every redirect leg. https://crbug.com/455099.
+  </summary>
+</histogram>
+
 <histogram name="Net.HttpResponseCode">
   <owner>mmenke@chromium.org</owner>
   <summary>The count of HTTP Response codes encountered.</summary>
@@ -24258,6 +24267,15 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Net.HttpResponseContainsInvalidHeaderValuesInRFC7230"

[Alexei Svitkine (slow), 2015/12/17 19:53:23]

Nit: These are a bit hard to read. Maybe you can reformat as:

Net.HttpResponse.ContainsInvalidHeaderValuesInRFC7230
Net.HttpRequest.ContainsInvalidHeaderValuesInRFC7230

[hiroshige, 2015/12/22 06:33:50]

Done.

+    enum="Boolean">
+  <owner>hiroshige@chromium.org</owner>
+  <summary>
+    Whether a response contains invalid response header values in RFC 7230. This
+    is counted once for every redirect leg. https://crbug.com/455099.
+  </summary>
+</histogram>
+
 <histogram name="Net.HttpResponseInfo.ConnectionInfo" enum="ConnectionInfo">
   <owner>bnc@chromium.org</owner>
   <summary>