Add metrics for paths in file scheme exceptions in content settings.

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 0a1e303f151319f2775300e4f53ae036cc5b3e60..796f0cb7b5cb511f7c2467bd437cc486c170939e 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -6809,6 +6809,34 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="ContentSettings.ExceptionSchemeFile.HasPath" enum="Boolean">

[Ilya Sherman, 2016/09/27 00:54:34]

nit: Please define a custom enum, BooleanHasPath, with more semantically
contentful labels.

[alexmos, 2016/09/27 01:11:22]

Done.

+  <owner>alexmos@chromium.org</owner>
+  <summary>
+    Records how often a content settings exception for the file: scheme has a
+    non-empty path. Recorded at browser start.

[Ilya Sherman, 2016/09/27 00:54:33]

nit: Probably worth mentioning explicitly that this is recorded *once per
exception* at browser start.  Ditto for the other metrics.

[alexmos, 2016/09/27 01:11:22]

Done.

+  </summary>
+</histogram>
+
+<histogram name="ContentSettings.ExceptionSchemeFile.TypeWithoutPath"
+    enum="ContentType">
+  <owner>alexmos@chromium.org</owner>
+  <summary>
+    Count of how often a specific content type has a content settings exception
+    defined for a file: scheme with no path (i.e., wildcard path). Recorded at
+    browser start.
+  </summary>
+</histogram>
+
+<histogram name="ContentSettings.ExceptionSchemeFile.TypeWithPath"
+    enum="ContentType">
+  <owner>alexmos@chromium.org</owner>
+  <summary>
+    Count of how often a specific content type has a content settings exception
+    defined for a file: scheme with a valid, non-empty path. Recorded at browser
+    start.
+  </summary>
+</histogram>
+
 <histogram name="ContentSettings.LastSettingParsed" enum="LastSettingParsed">
   <obsolete>
     Deprecated 2015-10-05 in Issue 433475. Histogram was used temorarily for