Vulkan: Implement simple render-to-texture.

This was mostly working already, just needed to set up a few entry
points.

BUG=angleproject:2200

Change-Id: I9c13d6d4dd42f23c69a58e42e07e3e28877671a1
Reviewed-on: https://chromium-review.googlesource.com/734237
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Frank Henigman <fjhenigman@chromium.org>
diff --git a/src/libANGLE/renderer/vulkan/RendererVk.cpp b/src/libANGLE/renderer/vulkan/RendererVk.cpp
index 9580e35..749733b 100644
--- a/src/libANGLE/renderer/vulkan/RendererVk.cpp
+++ b/src/libANGLE/renderer/vulkan/RendererVk.cpp
@@ -533,6 +533,7 @@
     outCaps->maxElementIndex              = std::numeric_limits<GLuint>::max() - 1;
     outCaps->maxFragmentUniformVectors    = 8;
     outCaps->maxVertexUniformVectors      = 8;
+    outCaps->maxColorAttachments          = 1;
 
     // Enable this for simple buffer readback testing, but some functionality is missing.
     // TODO(jmadill): Support full mapBufferRange extension.