Use SkFlatDictionary in SkGPipe to take advantage of its new features.

Use SkFlatDictionary in SkGPipe to take advantage of its new features.

Add a controller class to perform the allocation/unallocation for the dictionary and to provide an entry to be replaced, if replacements are allowed.

TODO:
Use LRU caching in my custom controller so replacements will be done less often.
More refactoring on SkFlatDictionary so picture recording's use of the dictionary does not require going through the path to replace.

Review URL: https://codereview.appspot.com/6345102

git-svn-id: http://skia.googlecode.com/svn/trunk@4639 2bbb7eff-a529-9590-31e7-b0007b416f81