Vulkan: Fix UtilsVk invalidating Context descriptors.

Fixes a validation error and rendering artifact in the WebGL test:
textures/misc/tex-image-and-sub-image-2d-with-array-buffer-view

Only applies to masked clears when combined with draw calls using
uniforms or textures.

Also make it easier to inspect layer messages in the debugger.

Bug: angleproject:2912
Change-Id: I4561895439221581b9dbc341d6de5d5a6c2096aa
Reviewed-on: https://chromium-review.googlesource.com/c/1462056
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
diff --git a/src/libANGLE/renderer/vulkan/RendererVk.cpp b/src/libANGLE/renderer/vulkan/RendererVk.cpp
index 79a241a..9ce020a 100644
--- a/src/libANGLE/renderer/vulkan/RendererVk.cpp
+++ b/src/libANGLE/renderer/vulkan/RendererVk.cpp
@@ -288,15 +288,16 @@
         }
     }
 
-    bool isError = (messageSeverity & VK_DEBUG_UTILS_MESSAGE_SEVERITY_ERROR_BIT_EXT) != 0;
+    bool isError    = (messageSeverity & VK_DEBUG_UTILS_MESSAGE_SEVERITY_ERROR_BIT_EXT) != 0;
+    std::string msg = log.str();
 
     if (isError)
     {
-        ERR() << log.str();
+        ERR() << msg;
     }
     else
     {
-        WARN() << log.str();
+        WARN() << msg;
     }
 
     return VK_FALSE;