Add chrome.fileSystem.GetVolumeList().

This CL adds a method to list available volumes. It's available only to kiosk
apps running in kiosk session and to some whitelited component apps/extensions.

[email protected]  # chrome_extensions.js reviewed at cr/90486340.
TEST=browser_tests: *KioskTest*GetVolumeList*,
     *FileSystemApiTestForRequestFileSystem*GetVolumeList*
BUG=440674

Review URL: https://codereview.chromium.org/1029803004

Cr-Commit-Position: refs/heads/master@{#324040}
diff --git a/extensions/browser/extension_function_histogram_value.h b/extensions/browser/extension_function_histogram_value.h
index 09707ce..3eb1b99 100644
--- a/extensions/browser/extension_function_histogram_value.h
+++ b/extensions/browser/extension_function_histogram_value.h
@@ -1056,6 +1056,7 @@
   LAUNCHERSEARCHPROVIDER_SETSEARCHRESULTS,
   DATAREDUCTIONPROXY_CLEARDATASAVINGS,
   BLUETOOTHPRIVATE_SETDISCOVERYFILTER,
+  FILESYSTEM_GETVOLUMELIST,
   // Last entry: Add new entries above and ensure to update
   // tools/metrics/histograms/histograms.xml.
   ENUM_BOUNDARY