The decision to enable caching or not was based on the size of the cache
as directed by eglProgramCacheResizeANGLE, which is incorrect for
applications that only use the ANDROID_blob_cache extension.

The new behavior is as follows:

- If EGL_CONTEXT_PROGRAM_BINARY_CACHE_ENABLED_ANGLE is specifically
  requested and set to true, but the size of the cache is 0, caching is
  disabled for the context.
- If EGL_CONTEXT_PROGRAM_BINARY_CACHE_ENABLED_ANGLE is specifically
  requested and set to false, caching is disabled for the context.
- Otherwise, caching is left enabled for the context, although the cache
  possibly has a size of zero, which effectively disables it.  During
  application execution, if the blob cache callbacks are set, the
  application cache will be used.

Bug: 896406, angleproject:2516
Change-Id: Ic0cabda03fb6bf53994e86e3ede30afc8021d67e
Reviewed-on: https://chromium-review.googlesource.com/c/1405708
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>