First implementation of chrome.platformKeys.

This change adds the selectClientCertificates() and subtleCrypto() functions and is missing the getKeyPair() function.
It is also missing the certificate permissions per extension and any UI changes.

BUG=450167

Review URL: https://codereview.chromium.org/875373002

Cr-Commit-Position: refs/heads/master@{#314625}
diff --git a/extensions/browser/extension_function_histogram_value.h b/extensions/browser/extension_function_histogram_value.h
index ab2f8af..b7a999e5 100644
--- a/extensions/browser/extension_function_histogram_value.h
+++ b/extensions/browser/extension_function_histogram_value.h
@@ -1015,6 +1015,7 @@
   EXTENSIONVIEWINTERNAL_NAVIGATE,
   NETWORKING_CONFIG_SETNETWORKFILTER,
   NETWORKING_CONFIG_FINISHAUTHENTICATION,
+  PLATFORMKEYSINTERNAL_SELECTCLIENTCERTIFICATES,
   // Last entry: Add new entries above and ensure to update
   // tools/metrics/histograms/histograms.xml.
   ENUM_BOUNDARY