Support offscreen contexts which own their backing surface

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 9c9f420bbef0707ac92f31ea18e7046caecb0477..cff4d8d9315697c7c5d88d654df0220ad534026b 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -97332,6 +97332,7 @@ value.
   <int value="-290672626" label="enable-asm-wasm"/>
   <int value="-288316828" label="enable-delegated-renderer"/>
   <int value="-279920685" label="affiliation-based-matching:enabled"/>
+  <int value="-279493876" label="WebVRExperimentalRendering:enabled"/>
   <int value="-278347667" label="default-tile-height"/>
   <int value="-277144896" label="enable-viewport-meta"/>
   <int value="-268357961" label="enable-feature-policy"/>
@@ -97427,6 +97428,7 @@ value.
   <int value="189728101" label="FasterLocationReload:disabled"/>
   <int value="194573877" label="MacViewsNativeDialogs:disabled"/>
   <int value="194895489" label="passive-listeners-default"/>
+  <int value="200347243" label="WebVRExperimentalRendering:disabled"/>
   <int value="201343576" label="enable-password-change-support:enabled"/>
   <int value="203776499" label="enable-virtual-keyboard-overscroll"/>
   <int value="223662457" label="BackgroundLoadingForDownloads:enabled"/>