Add an IPC method for Blink to call RapporService::RecordSample()

tools/metrics/rappor/rappor.xml

Index: tools/metrics/rappor/rappor.xml
diff --git a/tools/metrics/rappor/rappor.xml b/tools/metrics/rappor/rappor.xml
index c10a4189babcc116eaf2a15cd41bd644572da2d2..49b1f1ee583f87f39df1be550779256a6360dd9b 100644
--- a/tools/metrics/rappor/rappor.xml
+++ b/tools/metrics/rappor/rappor.xml
@@ -356,6 +356,22 @@ components/rappor/rappor_service.cc.
   </summary>
 </rappor-metric>
 
+<rappor-metric name="WebComponents.DocumentRegisterElement"

[Alexei Svitkine (slow), 2015/04/07 21:01:56]

This CL doesn't actually implement these, right?

If so probably better to have them in a separate CL that can be reviewed
together with the CL adding them.

[kojii, 2015/04/08 07:21:23]

Done, the CL is at https://codereview.chromium.org/1071463003/, and updated the
description.

+    type="ETLD_PLUS_ONE">
+  <owner>kojii@chromium.org</owner>
+  <summary>
+    The host of a URL that used Document::RegisterElement().
+  </summary>
+</rappor-metric>
+
+<rappor-metric name="WebComponents.ElementCreateShadowRoot"
+    type="ETLD_PLUS_ONE">
+  <owner>kojii@chromium.org</owner>
+  <summary>
+    The host of a URL that used Element::CreateShadowRoot().
+  </summary>
+</rappor-metric>
+
 <rappor-metric name="interstitial.harmful.domain" type="COARSE_RAPPOR_TYPE">
   <owner>nparker@chromium.org</owner>
   <summary>