Revert 281130 "Replace "external_install" boolean parameter with..."

Revert 281130 "Replace "external_install" boolean parameter with..."

Reason for revert:
Speculative revert, PlatformAppBrowserTest.Messaging test is broken: http://goo.gl/nYCK6a 

> Replace "external_install" boolean parameter with explicit enumeration in ExtensionUninstall method.
> 
> The intent is to be able to address issues found in https://code.google.com/p/chromium/issues/detail?id=84556#c39
> 
> * This change should be a strict refactoring, and there should be no change of behavior wrt to extension uninstall behavior.
> 
> * Identify a few specific reasons for extension uninstall and create enum values for them.
> 
> * Run "git cl format"
> 
> 
> BUG=84556
> TBR=sky@chromium.org for trivial changes under chrome/browser, except chrome/browser/extensions (already lgtm'ed).
> 
> Review URL: https://codereview.chromium.org/284103002

TBR=rpaquay@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=281227

[Nikita (slow), 2014-07-03 09:25:19]

Committed patchset #1 manually as r281227 (tree was closed).

[Nikita (slow), 2014-07-03 13:41:02]

Ok so test is still failing (http://goo.gl/jfJxhL), I'm placing this commit
back.