The functionality of MemoryProgramCache is divided up in two.  BlobCache
is now a generic binary cache, which interfaces with the callbacks from
EGL_ANDROID_blob_cache.  MemoryProgramCache handles program
[de]serialization and interacts with BlobCache.

Bug: angleproject:2516
Change-Id: Ie4328a2e56a26338e033d84f4e53a1103411937d
Reviewed-on: https://chromium-review.googlesource.com/1194285
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>