Revert 222074 "Refactor KeySystems code to call a function to po..."

Revert 222074 "Refactor KeySystems code to call a function to po..."

Revision 222074 did not go through the commit queue. Failing
contet_unittests on win-aura:

  KeySystemsTest.ClearKey_Basic
  KeySystemsTest.ClearKey_Parent
  KeySystemsTest.ExternalClearKey_Parent
  KeySystemsTest.Widevine_Basic
  KeySystemsTest.Widevine_Parent

> Refactor KeySystems code to call a function to populate the info. (re-land r221932)
> 
> This allows KeySystems to call GetContentClient()->AddKeySystems() so we can
> move key system information to chrome/. The new ContentClient API is defined and
> called, but we still rely on key_systems_info.cc.
> 
> BUG=224793
> TEST=Existing content_unittests and content_browsertests pass.
> TBR=jam@chromium.org
> 
> Review URL: https://codereview.chromium.org/23484019

TBR=ddorwin@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=222091

[please use gerrit instead, 2013-09-09 21:20:33]

Committed patchset #1 manually as r222091.