Add an autotest private api for installing Plugin VM

This CL adds chrome.autotestPrivate.installPluginVM(), which will
install and then launch Plugin VM. The arguments to this function would
be set by policy under normal operation, but we manually set these as
we cannot yet set policy from tast.

Bug: 1006664
Change-Id: Ia3556f960b6f4cdccf8012eaff1ff16e9cdc7ba3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1900524
Reviewed-by: Steven Bennetts <[email protected]>
Reviewed-by: Julian Watson <[email protected]>
Commit-Queue: Timothy Loh <[email protected]>
Cr-Commit-Position: refs/heads/master@{#717945}
diff --git a/extensions/browser/extension_function_histogram_value.h b/extensions/browser/extension_function_histogram_value.h
index 9717deb..33318591 100644
--- a/extensions/browser/extension_function_histogram_value.h
+++ b/extensions/browser/extension_function_histogram_value.h
@@ -1478,6 +1478,7 @@
   TERMINALPRIVATE_GETSETTINGS = 1415,
   TERMINALPRIVATE_SETSETTINGS = 1416,
   WEBSTOREPRIVATE_REQUESTEXTENSION = 1417,
+  AUTOTESTPRIVATE_INSTALLPLUGINVM = 1418,
   // Last entry: Add new entries above, then run:
   // python tools/metrics/histograms/update_extension_histograms.py
   ENUM_BOUNDARY