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 8033dc1a312efb69184a972bf135e986c33a3cb2..7274e73717618bc0b800cccecca926d5acb26b7e 100644
--- a/content/gpu/BUILD.gn
+++ b/content/gpu/BUILD.gn
@@ -77,4 +77,8 @@ source_set("gpu_sources") {
   if (use_x11) {
     deps += [ "//ui/events/platform/x11" ]
   }
+
+  if (enable_vulkan) {
+    deps += [ "//gpu/vulkan" ]
+  }
 }