Vulkan: Implement basic Clear and ReadPixels.

This enables the simple operations clear test on Vulkan. The current
implementation is very synchronous - it will block and finish the
current command buffer if there is any possibility of a race.

BUG=angleproject:1319

Change-Id: If01fe9a19ed6f539639a38786193d3626164cada
Reviewed-on: https://chromium-review.googlesource.com/367754
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
diff --git a/src/tests/gl_tests/RendererTest.cpp b/src/tests/gl_tests/RendererTest.cpp
index 8d6bf91..20be05f 100644
--- a/src/tests/gl_tests/RendererTest.cpp
+++ b/src/tests/gl_tests/RendererTest.cpp
@@ -145,16 +145,11 @@
         return;
     }
 
-    // TODO(jmadil): Vulkan clear.
-    if (IsVulkan())
-    {
-        std::cout << "Vulkan clears not yet implemented" << std::endl;
-        return;
-    }
-
     glClearColor(0.0f, 1.0f, 0.0f, 1.0f);
     glClear(GL_COLOR_BUFFER_BIT);
     EXPECT_PIXEL_EQ(0, 0, 0, 255, 0, 255);
+
+    ASSERT_GL_NO_ERROR();
 }
 
 // Select configurations (e.g. which renderer, which GLES major version) these tests should be run against.