Add an about://flags entry for enable/disable memory coordinator

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 7a8821eb2020ff0e2ca1b2ec8629647b5964102e..f492265fc1f1fbdbe6c0c2181720063dabea28f1 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -91302,6 +91302,7 @@ value.
   <int value="48159177" label="reduced-referrer-granularity"/>
   <int value="51793504" label="protect-sync-credential-on-reauth:disabled"/>
   <int value="56723110" label="enable-webfonts-intervention"/>
+  <int value="57791920" label="MemoryCoordinator:enabled"/>
   <int value="59784035" label="ImeThread:disabled"/>
   <int value="61205887" label="enable-text-input-focus-manager"/>
   <int value="64942701" label="OfflinePagesSvelteConcurrentLoading:disabled"/>
@@ -91611,6 +91612,7 @@ value.
   <int value="1548776701" label="AllBookmarks:disabled"/>
   <int value="1548942246" label="PassiveDocumentEventListeners:disabled"/>
   <int value="1560188739" label="reader-mode-heuristics"/>
+  <int value="1579461102" label="MemoryCoordinator:disabled"/>
   <int value="1586022426" label="AutofillCreditCardAssist:enabled"/>
   <int value="1589341623" label="disable-easy-unlock"/>
   <int value="1612446645" label="enable-weak-memorycache"/>