[Memory-UMA] Implement basic working prototype.

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 adcd8d1e373350d847d7645fd4ca760973aef4fb..b81075bc70542c4d4e0771e8d67ad867f49ed870 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -84305,6 +84305,8 @@ 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>
@@ -86294,6 +86296,8 @@ 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>
@@ -91079,6 +91083,8 @@ 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."/>