Mark fallback fonts in new Android font config parser

Mark fallback fonts in new Android font config parser

The new Android fonts.xml format doesn't explicitly tag fallback
fonts, or separate them from system fonts by putting them in a
separate file. We're assuming that any nameless font is a fallback
font.

Adds a unit test to track that we see as many fallback fonts as
expected when parsing a file.

BUG=chromium:400801
R=djsollen@google.com,bungeman@google.com

Committed: https://skia.googlesource.com/skia/+/2ed49a492bd7cfcfe1380476d270ce0afe0c8305

[tomhudson, 2014-08-13 14:01:49]

Test to catch the error that Derek pointed out.

Actual implementation is a 2-line change: set bool to true, set it to false if
we find a name. We make true the default, but we'd have to then set it to false
in every alias. The 3-line version doesn't strike me as particularly clearer?

[djsollen, 2014-08-13 14:37:58]

lgtm

[tomhudson, 2014-08-13 14:45:28]

The CQ bit was checked by tomhudson@google.com

[commit-bot: I haz the power, 2014-08-13 14:45:48]

CQ is trying da patch. Follow status at
 https://skia-tree-status.appspot.com/cq/tomhudson@chromium.org/468893002/1

[commit-bot: I haz the power, 2014-08-13 14:53:54]

Committed patchset #1 (1) as 2ed49a492bd7cfcfe1380476d270ce0afe0c8305