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 c17c5e63d071ebcc9caeb8190a071529f5898ff9..c9ce2572fd82a09fbfcdaa1a1ee8793d351891c0 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -19444,6 +19444,13 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="FileReaderSync.WorkerType" enum="FileReaderSyncWorkerType">
+  <owner>mek@chromium.org</owner>
+  <summary>
+    How often which worker types create FileReaderSync instances.

[Mark P, 2017/02/10 22:56:42]

how about?  (how often -> Records; create -> creates)
Records which worker types creates FileReaderSync instances.

I assume this is recorded on every time a FileReaderSync variable is
constructed.  Can you please add a sentence here explaining roughly when that
happens?

[Marijn Kruisselbrink, 2017/02/10 23:17:28]

I personally find that description a lot less clear... I'd like to at least keep
it explicit that this counts how many instances of FileReaderSync are created.
Also every histogram records something, so it seems kind of pointless to mention
that in the description (okay, every histogram also records how often something
happens, so maybe that's extraneous too, but I do believe that makes it clearer
what is recorded).

If you still think it needs rephrasing, maybe "For each FileReaderSync instance
records the type of the worker that created the instance."?
Not sure what you're asking me to do? A FileReaderSync instances is constructed
whenever a FileReaderSync instance is created. It's not like there is any kind
of explanation for when websites do that.

[Mark P, 2017/02/10 23:42:35]

I like that a lot better.  The reason for my original objection is that starting
a histogram description off with "How often" or "how many" makes readers think
it's going to be a count histogram, where the value emitted is a number, not an
enum histogram.  Thus, I'd like to avoid that original phrasing.
Well, you gave me a partial answer: it's *web sites* that create an instance.  I
didn't know that before from the description.  Can each website create more than
one instance, or is there roughly at most one instance ever associated with a
web site at one time?  If they create more than one, this is common, e.g., are
web sites that use this API creating many on each page load?  Basically, I'm
looking for a rough idea of when / how often these things are expected to be
created.

[Marijn Kruisselbrink, 2017/02/11 00:09:20]

Okay, makes sense. Changed description.
Basically, we have no idea what websites are doing with this API. The point in
adding the histogram is to try to get such an idea (and more specifically,
ideally the use counter would be enough, but I'd like to backport this to M57,
in which the use counters aren't and won't be able to collect data from most
workers, which is the only place this web API is exposed). I changed "workers"
to "web workers" in the description, to hopefully make it clearer that it's
websites using this.

Btw, was the histogram guidelines doc ever shared on chromium-dev? Seems like
that could be useful, especially as it has a bunch of advise/policies that as
far as I know weren't strongly enforced (or certainly not documented) earlier.
Making sure people know about the policies could probably help make reviews go
more smoothly...

[Mark P, 2017/02/11 05:00:04]

No, it wasn't.  That's a good idea.  Thanks!  I'll do it sometime this month.

+  </summary>
+</histogram>
+
 <histogram name="FileSystem.DirectoryDatabaseInit"
     enum="FileSystemDatabaseInitResult">
   <owner>tzik@chromium.org</owner>
@@ -91121,6 +91128,7 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
       label="HTMLIFrameElementAllowfullscreenAttributeSetAfterContentLoad"/>
   <int value="1806" label="PointerEventSetCaptureOutsideDispatch"/>
   <int value="1807" label="NotificationPermissionRequestedInsecureOrigin"/>
+  <int value="1808" label="V8FileReaderSync_Constructor"/>
 </enum>
 
 <enum name="FetchRequestMode" type="int">
@@ -91960,6 +91968,13 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <int value="6" label="File could not be exclusively opened."/>
 </enum>
 
+<enum name="FileReaderSyncWorkerType" type="int">
+  <int value="0" label="Dedicated Worker"/>
+  <int value="1" label="Shared Worker"/>
+  <int value="2" label="Service Worker"/>
+  <int value="3" label="Other"/>
+</enum>
+
 <enum name="FileSystemDatabaseInitResult" type="int">
   <int value="0" label="OK"/>
   <int value="1" label="Corruption"/>