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 1593ac61faa52e966e6e23b3d7808b92026939b9..7c9cbd3309ebd28ca5d199e19f7175d9a89fa062 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -22736,6 +22736,15 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Net.HttpRequestHeaderValueValidInRFC7230" enum="BooleanValid">
+  <owner>hiroshige@chromium.org</owner>
+  <summary>
+    The count of request header values valid/invalid in RFC 7230 (somehow
+    inaccurate because a header value can be counted multiple times).
+    https://crbug.com/455099.
+  </summary>
+</histogram>
+
 <histogram name="Net.HttpResponseCode">
   <owner>mmenke@chromium.org</owner>
   <summary>The count of HTTP Response codes encountered.</summary>
@@ -22749,6 +22758,15 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Net.HttpResponseHeaderValueValidInRFC7230" enum="BooleanValid">
+  <owner>hiroshige@chromium.org</owner>
+  <summary>
+    The count of response header values valid/invalid in RFC 7230 (somehow
+    inaccurate because a header value can be counted multiple times).
+    https://crbug.com/455099.
+  </summary>
+</histogram>
+
 <histogram name="Net.HttpServerProperties.UpdatePrefs"
     enum="HttpServerPropertiesUpdatePrefsLocation">
   <owner>rtenneti@chromium.org</owner>