SpirvShaderSampling: Fix flaky tests.

The cache keys were colliding, causing mayhem.
Add 32-bit unique keys to ImageViews and Samplers, combine them into a unique 64 bit key.

Bug: b/131246679
Change-Id: I74c86a80ee5fec1c97eda720bd0797bff4a1a7e0
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/29934
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Reviewed-by: Chris Forbes <chrisforbes@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Ben Clayton <bclayton@google.com>

src/Vulkan/VkSampler.cpp

diff --git a/src/Vulkan/VkSampler.cpp b/src/Vulkan/VkSampler.cpp
new file mode 100644
index 0000000..d80f699
--- /dev/null
+++ b/src/Vulkan/VkSampler.cpp
@@ -0,0 +1,23 @@
+// Copyright 2019 The SwiftShader Authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+
+#include "VkSampler.hpp"
+
+namespace vk
+{
+
+std::atomic<uint32_t> Sampler::nextID(1);
+
+} // namespace vk