Add support for letter tile avatars to ContactsPhotoManager

* Add LetterTileDrawable, a custom drawable used to display letter tiles
for contacts without a contact photo, instead of static bitmap resource
drawables.

* Add a class DefaultImageRequest to ContactPhotoManager. This is essentially
a data holder object used to store and retrieve various parameters that
clients can use to configure the way they want their requested letter tile
avatars to be drawn.

* Add LetterTileImageProvider to ContactPhotoManager. LetterTileImageProvider
extends DefaultImageProvider, but returns instances of LetterTileDrawable
instead of BitmapDrawables when a default contact image is needed.

* Add two new APIs to ContactPhotoManager:
getDefaultAvatarForContact - This returns an instance of a LetterTileDrawable,
configured with the display parameters stored in the provided
DefaultImageRequest.
getDefaultAvatarUriForContact - This returns an uri which the
ContactPhotoManager can use to recreate a DefaultImageRequest and hence
a LetterTileDrawable.

* Modify ContactPhotoManager.loadPhoto and loadThumbnail to accept a
DefaultImageRequest as a parameter.

* Modify the following classes to use the new ContactPhotoManager APIs. These
affect both the Dialer and People apps.
ContactEntryListADapter
ContactListAdapter
ContactTileView
PhoneNumberListAdapter

Bug: 13101785
Change-Id: Id1a87b459d6e63c42049739059a3b3ee202af837
diff --git a/res/values/strings.xml b/res/values/strings.xml
index d4bb1ff..c63fb33 100644
--- a/res/values/strings.xml
+++ b/res/values/strings.xml
@@ -726,4 +726,7 @@
     <!-- Attribution of a contact status update, when the time of update is known -->
     <string name="contact_status_update_attribution_with_date"><xliff:g id="date" example="3 hours ago">%1$s</xliff:g> via <xliff:g id="source" example="Google Talk">%2$s</xliff:g></string>
 
+    <!-- Font family used when drawing letters for letter tile avatars.
+         Do not translate. -->
+    <string name="letter_tile_letter_font_family">sans-serif-thin</string>
 </resources>