Revert 266297 "1. Handle the case of empty embedder_extension_id..."

Revert 266297 "1. Handle the case of empty embedder_extension_id..."

This change introduces static initializers (the two
static const std::string Type constants).

Static strings should be declared as char * instead.

> 1. Handle the case of empty embedder_extension_id in    guestview.h.
> 
> 2. Introduce a template class GuestView<T> to handle the    *guestview-specific functions in guestview.h:
>    . Rename GuestView to GuestViewBase, introduce GuestView<T> class, and move *ViewGuest-specific functions to     GuestView<T>:
>         -- FromWebContents<T>(...)
>         -- From<T>(...).
>    . Introduce a template member function As() in      GuestViewBase to replace all of the As*View functions.
> 
> 3. In each derived *ViewGuest class , e.g., WebViewGuest &    AdViewGuest, define a static variable to show its view type    (string).
> 
> 
> BUG=351824
> 
> Review URL: https://codereview.chromium.org/237533008

TBR=hanxi@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=266313

[rmsousa, 2014-04-26 01:20:53]

Committed patchset #1 manually as r266313 (tree was closed).