Implement <webview>.addContentScript/removeContentScript API [1].

This patch includes the changes that enables <webview>.addContentScript/removeContentScript API  work on extensions.

This is the first patch in a series of patches:
1) Implement <webview>.addContentScript/removeContentScript API [1] (https://codereview.chromium.org/959413003)
2) Implement <webview>.addContentScript/removeContentScript API [2] (https://codereview.chromium.org/1056533002)
3) Implement <webview>.addContentScript/removeContentScript API [3] (https://codereview.chromium.org/1058113002)

[email protected]
BUG=461052

Review URL: https://codereview.chromium.org/959413003

Cr-Commit-Position: refs/heads/master@{#325492}
diff --git a/extensions/browser/extension_function_histogram_value.h b/extensions/browser/extension_function_histogram_value.h
index ac0412a8..eb6ad0e 100644
--- a/extensions/browser/extension_function_histogram_value.h
+++ b/extensions/browser/extension_function_histogram_value.h
@@ -1062,6 +1062,8 @@
   DEVELOPERPRIVATE_UPDATEPROFILECONFIGURATION,
   SOCKETS_UDP_SETBROADCAST,
   FILEMANAGERPRIVATE_GETPROVIDINGEXTENSIONS,
+  WEBVIEWINTERNAL_ADDCONTENTSCRIPTS,
+  WEBVIEWINTERNAL_REMOVECONTENTSCRIPTS,
   // Last entry: Add new entries above and ensure to update
   // tools/metrics/histograms/histograms.xml.
   ENUM_BOUNDARY