Low memory page navigation GC for low end devices

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 b3245a13eda9e1add3dc5adc8e4802ab5db42060..2ac1f16a4278503c41cc60bcb17d9756fca6a30d 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -27418,6 +27418,14 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="LowMemoryPageNavigationGC.Reduction" units="MB">

[Ilya Sherman, 2017/06/26 18:48:37]

It looks like you're adding a new top-level group name,
"LowMemoryPageNavigationGC".  Could you please use one of the existing group
names as well; or create a more general top-level group if you think a new one
is really most appropriate?

[keishi, 2017/06/27 03:44:53]

Done. Used BlinkGC top level group.

+  <owner>keishi@chromium.org</owner>
+  <summary>
+    Amount of memory (Blink GC + PA + V8 main thread isolate heap) reduced with
+    the low memory page navigation GC.

[Ilya Sherman, 2017/06/26 18:48:37]

It would be great to document this feature a wee bit more here: Is this a GC
that occurs following a page navigation?  Only on some types of devices?  Only
when memory is low?  I think just splitting this sentence into two or three, and
then filling in a few blanks, will help quite a lot.

[keishi, 2017/06/27 03:44:53]

Done.

+  </summary>
+</histogram>
+
 <histogram name="ManagedUsers.ChromeOS.PasswordChange"
     enum="ManagedUserPasswordChange">
   <owner>achuith@chromium.org</owner>