Added initial Vulkan build files as well as a basic implementation file.

content/gpu/BUILD.gn

Index: content/gpu/BUILD.gn
diff --git a/content/gpu/BUILD.gn b/content/gpu/BUILD.gn
index 3bc1845a82ee9a5685e7f1a7b7cd83f810bcfe6c..182be5e62dc68fe010ebf005ce7fd6b318cf55e0 100644
--- a/content/gpu/BUILD.gn
+++ b/content/gpu/BUILD.gn
@@ -76,4 +76,8 @@ source_set("gpu_sources") {
   if (use_x11) {
     deps += [ "//ui/events/platform/x11" ]
   }
+
+  if (enable_vulkan) {
+    deps += [ "//ui/vulkan" ]
+  }
 }