When rendering with no render target on D3D, two bugs lead to
incorrect behavior on Intel drivers < 4815. The rendering samples
always pass neglecting discard statement in pixel shader.

Two bugs are listed bellow,
1. When a framebuffer has no attachments, the pixel shader will be
recompiled to drop 'SV_TARGET'. On Intel drivers, when using a pixel
shader with no 'SV_TARGET' in a draw, pixels are always generated even
if they should be discard by 'discard' statements.

2. When a framebuffer has no attachments, ID3D11BlendState.RenderTarget
[].RenderTargetWriteMask were set to 0 in angle. If RenderTargetWriteMask
is 0 and rendertarget is not set, then rendering samples also pass
neglecting discard statement in pixel shader on Intel.

So we add a dummy texture as render target to workaround this issue.

BUG=angleproject:2152

TEST=FramebufferTest_ES31.RenderingLimitToDefaultFBOSizeWithNoAttachments/ES3_1_D3D11
TEST=dEQP-GLES31.functional.fbo.no_attachments.*
TEST=dEQP-GLES31.functional.state_query.integer.max_framebuffer*
TEST=dEQP-GLES31.functional.state_query.integer.max_color_texture_samples_*
TEST=dEQP-GLES31.functional.state_query.integer.max_depth_texture_samples_*
TEST=dEQP-GLES31.functional.state_query.integer.max_integer_samples_*

Change-Id: I1cb974703b6c05c39b731d147f7c8c4fb7b5fe68
Reviewed-on: https://chromium-review.googlesource.com/741544Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>