Unify duplicated code for both depth and stencil buffer in ValidateBlitFramebufferParameters()
Unify duplicated code for both depth and stencil buffer in ValidateBlitFramebufferParameters()

Tested with angle_*_tests and WebGL CTS in Chrome Canary on Windows. Passed with no regressions.

Change-Id: Ied0a32ea75565ef19b8e87bed8bdd555b74edee3
Reviewed-on: https://chromium-review.googlesource.com/234110
Reviewed-by: Geoff Lang <b6fc25fe0362055230985c05cbfa8adb741ccc0f@chromium.org>
Reviewed-by: Shannon Woods <0f3694938fd5703bd548127ee497e4d604509bef@chromium.org>
Tested-by: Dongseong Hwang <140417d8a95a7b29c412635e9e450ff35ca54a3e@intel.com>
Reviewed-by: Kenneth Russell <1ebccd90c2bc76de65b6f830f2128a91ed69fdfb@chromium.org>

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