[bfcache] Record why BrowsingInstance wasn't swapped.

The number of cases where we can't cache the page due to related active
contents turned out to be higher than expected. Record metrics to
understand why this is happening.

[email protected],[email protected]
BUG=1026101

Change-Id: If4c291f0b6108edef4162b0abecbdb9f978c5805
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1923289
Commit-Queue: Alexander Timin <[email protected]>
Reviewed-by: Alex Moshchuk <[email protected]>
Reviewed-by: Arthur Sonzogni <[email protected]>
Cr-Commit-Position: refs/heads/master@{#716955}
diff --git a/content/browser/BUILD.gn b/content/browser/BUILD.gn
index 1cfed87..e016ec5 100644
--- a/content/browser/BUILD.gn
+++ b/content/browser/BUILD.gn
@@ -922,6 +922,7 @@
     "frame_host/render_frame_proxy_host.h",
     "frame_host/render_widget_host_view_guest.cc",
     "frame_host/render_widget_host_view_guest.h",
+    "frame_host/should_swap_browsing_instance.h",
     "frame_host/webui_navigation_throttle.cc",
     "frame_host/webui_navigation_throttle.h",
     "generic_sensor/sensor_provider_proxy_impl.cc",