Add new memory histograms which fix inprecise bucketing.

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 8a48a1b029da63e2d36369194ab1f8820d78aa90..6795dcf83689192281636f94096520cc953c9c0c 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -17251,8 +17251,20 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <owner>kenjibaheux@google.com</owner>
   <owner>kouhei@chromium.org</owner>
   <summary>
-    The sum of all processes' swap.  Recorded once per UMA ping if the system
-    has swapped.
+    The sum of all processes' swap. Recorded once per UMA ping if the system has
+    swapped. See Memory.Swap.Total2 for the same metric with higher precision
+    bucketing.
+  </summary>
+</histogram>
+
+<histogram name="Memory.Swap.Total2" units="MB">
+  <owner>hajimehoshi@chromium.org</owner>
+  <owner>kenjibaheux@google.com</owner>
+  <owner>kouhei@chromium.org</owner>
+  <owner>rkaplow@chromium.org</owner>
+  <summary>
+    The sum of all processes' swap. Recorded once per UMA ping if the system has
+    swapped.
   </summary>
 </histogram>
 
@@ -17280,7 +17292,22 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <owner>hajimehoshi@chromium.org</owner>
   <owner>kenjibaheux@google.com</owner>
   <owner>kouhei@chromium.org</owner>
-  <summary>The sum of all processes.  Recorded once per UMA ping.</summary>
+  <summary>
+    The sum of all processes. This is not aware of shared memory so it is just a
+    rough estimate. Recorded once per UMA ping. See Memory.Total2 for the same
+    metric with higher precision bucketing.
+  </summary>
+</histogram>
+
+<histogram name="Memory.Total2" units="MB">

[Alexei Svitkine (slow), 2015/08/04 18:37:44]

Should the unit be MiB?

+  <owner>hajimehoshi@chromium.org</owner>
+  <owner>kenjibaheux@google.com</owner>
+  <owner>kouhei@chromium.org</owner>
+  <owner>rkaplow@chromium.org</owner>
+  <summary>
+    The sum of all processes. This is not aware of shared memory so it is just a
+    rough estimate. Recorded once per UMA ping.
+  </summary>
 </histogram>
 
 <histogram name="Memory.Utility" units="KB">