- The scissor when clearing should not be clipped against the viewport.
- The render pass was created with a render area == to the current
viewport, but the viewport can be changed by the tests multiple times
per render pass, so we should always keep the renderArea to the full
framebuffer instead.
- Enables an additional 163 dEQP tests.
- We should clip the scissor to the framebuffer dimensions instead of
the viewport. Its valid to do a cmdClearAttachments outside the
viewport, but not outside the full framebuffer's dimension.

Bug: angleproject:2443

Change-Id: I79168e9f0c782d6dec77470fef938b85ad7a8794
Reviewed-on: https://chromium-review.googlesource.com/998448
Commit-Queue: Luc Ferron <lucferron@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>