Dawn: fix rendering to mipmapped textures.

Use a texture view with a mipLevelCount of 1 when using a texture
as an attachment.
Dawn validation will fail if the view has more than one mip.

Change-Id: I6a3594dade9f65fa8e713d433797414c6ba8ecec
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/249423
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Stephen White <senorblanco@chromium.org>

Author: SenorBlanco

src/gpu/dawn/GrDawnOpsRenderPass.cpp

@@ -59,7 +59,9 @@ dawn::RenderPassEncoder GrDawnOpsRenderPass::beginRenderPass(dawn::LoadOp colorO
     dawn::Texture texture = static_cast<GrDawnRenderTarget*>(fRenderTarget)->texture();
     auto stencilAttachment = static_cast<GrDawnStencilAttachment*>(
         fRenderTarget->renderTargetPriv().getStencilAttachment());
-    dawn::TextureView colorView = texture.CreateView();
+    dawn::TextureViewDescriptor desc;
+    desc.mipLevelCount = 1;
+    dawn::TextureView colorView = texture.CreateView(&desc);
     const float *c = fColorInfo.fClearColor.vec();
 
     dawn::RenderPassColorAttachmentDescriptor colorAttachment;