Dynamically generate a heading for Extension Docs API pages

chrome/common/extensions/docs/templates/json/api_availabilities.json

Index: chrome/common/extensions/docs/templates/json/api_availabilities.json
diff --git a/chrome/common/extensions/docs/templates/json/api_availabilities.json b/chrome/common/extensions/docs/templates/json/api_availabilities.json
new file mode 100644
index 0000000000000000000000000000000000000000..bd3a08d5b18e7fe8fec6e50d7cdaaab4e607ee4e
--- /dev/null
+++ b/chrome/common/extensions/docs/templates/json/api_availabilities.json
@@ -0,0 +1,6 @@
+{
+  "idle" : "6",
+  "contextMenus" : "6",
+  "tts" : "14",
+  "webstore" : "15"
+}

[not at google - send to devlin, 2013/04/27 01:48:34]

nice! I'm curious, what's preventing these APIs from being detected,
particularly contextMenus?

(and ... how are you determining the old ones?)

[epeterson, 2013/04/27 23:17:23]

Definitely take a look at how I'm using the _permission_features.json and
_manifest_features.json files in availability_data_source when you get the
chance.

These features files are only present until version 19 (although
_permission_features lacks the "channel" key for APIs, so I'm only going to
version 20).

Version 18 doesn't have either of these files, only individual API schemas.

From version 17 down to version 5, the extension_api.json file contains
namespaces for each API. I was looking at possibly using this to generate
availability for older APIs. It would work for idle, contextMenus, tts (webstore
is weird, though.. there's only webstorePrivate in the pre-18 versions), as well
as changing availability for APIs like tabs or windows from the current "20" to
a more accurate "5."

So, in summary, 
versions 20+ is what this patch currently handles
version 19 is a special case
version 18 is also a special case
versions 17-5 have extension_api.json files which could be used to find
availability for older APIs

[not at google - send to devlin, 2013/04/30 17:20:30]

My comment was more that contextMenus seems no more special-casey than say tabs
or windows. I'm wondering what makes it necessary to specify this.

Ah - and now I see, I presume it's because contextMenus.html contains version 6
manually.

Yep. I think, unfortunately, it will be tricky to push this patch since tabs
will show up as version 20. If it's not too much trouble, going to back to when
the APIs were added to extension_api.json would be nice... then again, it's (a)
never going to change and (b) will introduce some extra work (... if one-off)
for the server and (c) is probably going to be slower than just going back and
figuring out what changes between each version.

Actually... (c) I'm not so sure. I'll let you be the judge.