Pipe factory names independently from the flattenables using them.

Pipe factory names independently from the flattenables using them.

Avoids an issue where a flattenable written twice might be written
differently (the first time the flat data may have a name, whereas
the second time it will have an index).

Also add a test which confirms that identical flattenables will have
the same SkFlatData representation.

BUG=https://code.google.com/p/skia/issues/detail?id=721
TEST=FlatDataTest.cpp

Review URL: https://codereview.appspot.com/6431057

git-svn-id: http://skia.googlecode.com/svn/trunk@4896 2bbb7eff-a529-9590-31e7-b0007b416f81