Vulkan: Expose EXT_debug_marker and stub out the implementation.

This extension is used by Chrome.

BUG=angleproject:2853

Change-Id: Ie8d4ba07857c581a4ec3f90faabdf747b6b52445
Reviewed-on: https://chromium-review.googlesource.com/1246263
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>

src/libANGLE/renderer/vulkan/ContextVk.cpp

@@ -577,27 +577,27 @@ std::string ContextVk::getRendererDescription() const
 
 void ContextVk::insertEventMarker(GLsizei length, const char *marker)
 {
-    UNIMPLEMENTED();
+    // TODO: Forward this to a Vulkan debug marker.  http://anglebug.com/2853
 }
 
 void ContextVk::pushGroupMarker(GLsizei length, const char *marker)
 {
-    UNIMPLEMENTED();
+    // TODO: Forward this to a Vulkan debug marker.  http://anglebug.com/2853
 }
 
 void ContextVk::popGroupMarker()
 {
-    UNIMPLEMENTED();
+    // TODO: Forward this to a Vulkan debug marker.  http://anglebug.com/2853
 }
 
 void ContextVk::pushDebugGroup(GLenum source, GLuint id, GLsizei length, const char *message)
 {
-    UNIMPLEMENTED();
+    // TODO: Forward this to a Vulkan debug marker.  http://anglebug.com/2853
 }
 
 void ContextVk::popDebugGroup()
 {
-    UNIMPLEMENTED();
+    // TODO: Forward this to a Vulkan debug marker.  http://anglebug.com/2853
 }
 
 bool ContextVk::isViewportFlipEnabledForDrawFBO() const

src/libANGLE/renderer/vulkan/vk_caps_utils.cpp

@@ -45,6 +45,7 @@ void GenerateCaps(const VkPhysicalDeviceProperties &physicalDeviceProperties,
     outExtensions->textureStorage = true;
     outExtensions->framebufferBlit = true;
     outExtensions->copyTexture     = true;
+    outExtensions->debugMarker     = true;
 
     // TODO(lucferron): Eventually remove everything above this line in this function as the caps
     // get implemented.