Add Cross Process Guests feature switch to about:flags.

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 988fba13c4210a41bb63b9a41d0be3e8cc9ba8b7..28e4dde8bf9b8cc26a06c2513bff7b4787eeab79 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -91193,6 +91193,7 @@ value.
   <int value="203776499" label="enable-virtual-keyboard-overscroll"/>
   <int value="223662457" label="BackgroundLoadingForDownloads:enabled"/>
   <int value="244697230" label="enable-theme-color-in-tabbed-mode"/>
+  <int value="262382944" label="GuestViewCrossProcessFrames:disabled"/>
   <int value="266702296" label="disable-plugin-power-saver"/>
   <int value="270267831" label="enable-scripts-require-action"/>
   <int value="274103741" label="enable-ntp-popular-sites"/>
@@ -91533,6 +91534,7 @@ value.
   <int value="1865068568" label="disable-audio-support-for-desktop-share"/>
   <int value="1865799183" label="javascript-harmony"/>
   <int value="1867085340" label="brotli-encoding:enabled"/>
+  <int value="1878331098" label="GuestViewCrossProcessFrames:enabled"/>
   <int value="1881036528" label="disable-multilingual-spellchecker"/>
   <int value="1881174782" label="disable-brotli"/>
   <int value="1889076955" label="disable-app-link"/>