Add UMA memory metrics for V8 heap spaces

The corresponding UKM metrics already exist and were approved by
privacy team: https://goo.gl/X5eYHh

The metrics will help evaluate the upcoming young generation GC
optimizations.

Bug:1054771

Change-Id: I8caa8cce5e7b253aee76714f980a9ecd6242c530
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2130186Reviewed-by: Hannes Payer <hpayer@chromium.org>
Reviewed-by: Steven Holte <holte@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#755970}

tools/metrics/histograms/histograms.xml

@@ -196587,6 +196587,41 @@ regressions. -->
       label="Only counting objects allocated by V8 javascript engine."/>
   <suffix name="V8.Main.GlobalHandles"
       label="Memory used by V8 global handles in the main isolate."/>
+  <suffix name="V8.Main.Heap" label="Only counting memory used by V8 heap"/>
+  <suffix name="V8.Main.Heap.AllocatedObjects"
+      label="Only counting objects allocated in V8 heap"/>
+  <suffix name="V8.Main.Heap.CodeSpace"
+      label="Only counting memory used by the code-space of V8 heap"/>
+  <suffix name="V8.Main.Heap.CodeSpace.AllocatedObjects"
+      label="Only counting objects allocated in the map-space of V8 heap"/>
+  <suffix name="V8.Main.Heap.LargeObjectSpace"
+      label="Only counting memory used by the large-object-space of V8 heap"/>
+  <suffix name="V8.Main.Heap.LargeObjectSpace.AllocatedObjects"
+      label="Only counting objects allocated in the large-object-space of V8
+             heap"/>
+  <suffix name="V8.Main.Heap.MapSpace"
+      label="Only counting memory used by the map-space of V8 heap"/>
+  <suffix name="V8.Main.Heap.MapSpace.AllocatedObjects"
+      label="Only counting objects allocated in the code-space of V8 heap"/>
+  <suffix name="V8.Main.Heap.NewLargeObjectSpace"
+      label="Only counting memory used by the new-large-object-space of V8
+             heap"/>
+  <suffix name="V8.Main.Heap.NewLargeObjectSpace.AllocatedObjects"
+      label="Only counting objects allocated in the new-large-object-space of
+             V8 heap"/>
+  <suffix name="V8.Main.Heap.NewSpace"
+      label="Only counting memory used by the new-space of V8 heap"/>
+  <suffix name="V8.Main.Heap.NewSpace.AllocatedObjects"
+      label="Only counting objects allocated in the new-space of V8 heap"/>
+  <suffix name="V8.Main.Heap.OldSpace"
+      label="Only counting memory used by the old-space of V8 heap"/>
+  <suffix name="V8.Main.Heap.OldSpace.AllocatedObjects"
+      label="Only counting objects allocated in the old-space of V8 heap"/>
+  <suffix name="V8.Main.Heap.ReadOnlySpace"
+      label="Only counting memory used by the read-only-space of V8 heap"/>
+  <suffix name="V8.Main.Heap.ReadOnlySpace.AllocatedObjects"
+      label="Only counting objects allocated in the read-only-space of V8
+             heap"/>
   <affected-histogram name="Memory.Experimental.Browser2"/>
   <affected-histogram name="Memory.Experimental.Extension2"/>
   <affected-histogram name="Memory.Experimental.Gpu2"/>