Emit UMAs for private memory footprint.

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 0d4cb7e43506eeed00f04b999cec8f1075fbba90..6e625ea235357eaf6bf56c805517db995c906394 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -84089,6 +84089,8 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
 
 <histogram_suffixes name="BrowserMemoryAllocator2" separator=".">
   <suffix name="Resident" label="Only counting resident memory."/>
+  <suffix name="PrivateMemoryFootprint"
+      label="Only counting private resident + swapped/compressed memory."/>
   <suffix name="Malloc" label="Constrained to malloc allocator."/>
   <affected-histogram name="Memory.Experimental.Browser2"/>
 </histogram_suffixes>
@@ -86075,6 +86077,8 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
 
 <histogram_suffixes name="GpuMemoryAllocator2" separator=".">
   <suffix name="Resident" label="Only counting resident memory."/>
+  <suffix name="PrivateMemoryFootprint"
+      label="Only counting private resident + swapped/compressed memory."/>
   <suffix name="Malloc" label="Constrained to malloc allocator."/>
   <affected-histogram name="Memory.Experimental.Gpu2"/>
 </histogram_suffixes>
@@ -90809,6 +90813,8 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
 
 <histogram_suffixes name="RendererMemoryAllocator2" separator=".">
   <suffix name="Resident" label="Only counting resident memory."/>
+  <suffix name="PrivateMemoryFootprint"
+      label="Only counting private resident + swapped/compressed memory."/>
   <suffix name="Malloc" label="Constrained to malloc allocator."/>
   <suffix name="PartitionAlloc" label="Constrained to partition allocator."/>
   <suffix name="BlinkGC" label="Constrained to blink GC allocator."/>