Photo Picker dialog: Add UMA statistics.

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 838f9a1a91e81d15901f82eda0d30fb439f55296..2e430c1555bb2d2bb1c3d4d5e42bded9fb9460bd 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -937,6 +937,72 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Android.PhotoPicker.BitmapScalerTask" units="ms">
+  <owner>finnur@chromium.org</owner>
+  <owner>twellington@chromium.org</owner>
+  <summary>
+    Measures the amount of time the BitmapScaler spends scaling per bitmap.

[Mark P, 2017/06/02 17:17:58]

nit: per -> a
nit: spends -> spent

[Finnur, 2017/06/06 14:23:16]

Done.

+  </summary>
+</histogram>
+
+<histogram name="Android.PhotoPicker.CacheHits" units="Hits">
+  <owner>finnur@chromium.org</owner>
+  <owner>twellington@chromium.org</owner>
+  <summary>
+    Measures how often an image is served from the high-res cache while the

[Mark P, 2017/06/02 17:17:58]

see similar comments to DecodeRequests, as my same concerns apply here.
(Sorry I reviewed these histograms out of order.)

[Finnur, 2017/06/06 14:23:16]

No problem. Done (see answer below).

+    dialog is open.
+  </summary>
+</histogram>
+
+<histogram name="Android.PhotoPicker.DecodeRequests" units="Hits">
+  <owner>finnur@chromium.org</owner>
+  <owner>twellington@chromium.org</owner>
+  <summary>
+    Measures how often an image is sent for decoding while the dialog is open.

[Mark P, 2017/06/02 17:17:58]

nit: "how often" sounds like a rate.  You're simply measuring the number of
something.  Is a better / more accurate description
// The number of images sent for decoding upon opening the photo picker dialog.
Yet, that's not quite right because when this is recorded sounds odd.  It looks
like it's recorded on, say, cancel events too, which seems strange to me.

[Finnur, 2017/06/06 14:23:16]

Yeah, it's not a rate and it's not just counted while the dialog is being
opened. It is how many images are decoded during the lifetime of the dialog.
Example:

If the dialog fits 16 images and I close it right after it populates, then 16 is
the metric recorded.
If I don't close it right away, but scroll down so that 8 more images are shown,
then 24 is the metric recorded.
If I scroll back up again, 24 is still the number recorded, because the previous
images are cached and not sent for decoding again.

This explains why it is recorded on Cancel (or Browse, or whatever the final
action is that dismisses the dialog).

I've refined the comment.

[Mark P, 2017/06/07 17:19:30]

The revised comment reads great now!  thanks!

+  </summary>
+</histogram>
+
+<histogram name="Android.PhotoPicker.DialogAction"
+    enum="PhotoPickerDialogAction">
+  <owner>finnur@chromium.org</owner>
+  <owner>twellington@chromium.org</owner>
+  <summary>
+    Records which action the user takes in the PhotoPickerDialog.

[Mark P, 2017/06/02 17:17:58]

Do you have a normalizing action or histogram that show how often is photo
picker dialog is opened?

[Finnur, 2017/06/06 14:23:16]

Not sure I need it. The main purpose of this metric is to see if a large portion
of users are opting for the escape hatch ('Browse' to pick a photo from the
Android Stock Picker) instead of performing an action in our dialog. So, I'm
purely comparing against other actions taken, and as I understand it, this
metric provides that. In short, I just need to be able to see: X% of time
'Browse' was picked. Also, I believe the current list of actions is an
exhaustive list of outcomes in the dialog, so I'm guessing that *if* I need the
open count at some point in the future, then I can just add up all the counters
in this metric (or add a separate metric for that).

[Mark P, 2017/06/07 17:19:31]

Acknowledged.  Good to know that the current list of actions is (or is
effectively) exhaustive so you don't need a normalizing value.

+  </summary>
+</histogram>
+
+<histogram name="Android.PhotoPicker.ImageByteCount" units="KB">
+  <owner>finnur@chromium.org</owner>
+  <owner>twellington@chromium.org</owner>
+  <summary>Measures the byte count of a decoded image.</summary>

[Mark P, 2017/06/02 17:17:58]

ditto my comments on ImageDecodeTime

[Finnur, 2017/06/06 14:23:16]

Done (see answer below).

+</histogram>
+
+<histogram name="Android.PhotoPicker.ImageDecodeTime" units="ms">
+  <owner>finnur@chromium.org</owner>
+  <owner>twellington@chromium.org</owner>
+  <summary>
+    Measures the amount of time it takes the decoder to decode one image.

[Mark P, 2017/06/02 17:17:58]

Only recorded on success or always recorded?

Also, what's with the "!= -1" in the code?  It's  clearly not decoded under the
same conditions as RequestProcessTime, yet the descriptions need as if they're
emitted under the same conditions.  If they're under different conditions,
please be clear:
"Only recorded if ..."

[Finnur, 2017/06/06 14:23:16]

RequestProcessTime is for measuring the length of time it takes to satisfy a
single decode request, including rpc delays and all. As such, it was not
intended to only be recorded on success, but I guess it could be argued either
way and I could be convinced to record it only on success. Until then, I've
revised the comment.

ImageDecodeTime and ImageByteCount only make sense on successful decode, so I've
revised those comment also.

+  </summary>
+</histogram>
+
+<histogram name="Android.PhotoPicker.RequestProcessTime" units="ms">
+  <owner>finnur@chromium.org</owner>
+  <owner>twellington@chromium.org</owner>
+  <summary>
+    Measures the amount of time it takes to process one decode request end to
+    end (RPC and actual decoding of the bits by utility process).

[Mark P, 2017/06/02 17:17:58]

Only recorded on success or always recorded?

[Finnur, 2017/06/06 14:23:16]

Done.

+  </summary>
+</histogram>
+
+<histogram name="Android.PhotoPicker.UpscaleLowResBitmap" units="ms">
+  <owner>finnur@chromium.org</owner>
+  <owner>twellington@chromium.org</owner>
+  <summary>
+    Measures the amount of time it takes to upscale a bitmap from the low-res
+    cache.

[Mark P, 2017/06/02 17:17:58]

optional nit: explain roughly under what conditions this is emitted, e.g., every
time this bitmap is viewed? Only the first time?

[Finnur, 2017/06/06 14:23:16]

Revised.

+  </summary>
+</histogram>
+
 <histogram name="Android.PrepareMenu.OpenWebApkVisibilityCheck" units="ms">
   <owner>hanxi@chromium.org</owner>
   <owner>pkotwicz@chromium.org</owner>