Move ExtensionActionStorageManager out of extension_action_api.*
There's really no reason to have these in the same file, and it's cluttering it
up.
Bonus:
- Convert ExtensionActionStorageManager to use a BrowserContext.
- Remove ExtensionActionStorageManager's ExtensionService dependency.
- Remove ExtensionActionStorageManager's public weak ptr interface
- Consolidate extension_misc:: ExtensionAction icon stuff and ExtensionActionAPI
icon stuff.
BUG=407290
Review URL: https://codereview.chromium.org/
502033003
Cr-Commit-Position: refs/heads/master@{#292036}