Rename VulkanViewer to Viewer, take 2.

tools/viewer/Application.h

Index: tools/viewer/Application.h
diff --git a/tools/vulkan/Application.h b/tools/viewer/Application.h
similarity index 89%
rename from tools/vulkan/Application.h
rename to tools/viewer/Application.h
index 4504d177e48974697256a21bd5afe744276f1168..235ff09ed4ed73e7b78ce5d958ecde27d0d54104 100644
--- a/tools/vulkan/Application.h
+++ b/tools/viewer/Application.h
@@ -8,6 +8,8 @@
 #ifndef Application_DEFINED
 #define Application_DEFINED
 
+namespace sk_app {
+
 class Application {
 public:
     static Application* Create(int argc, char** argv, void* platformData);
@@ -17,4 +19,6 @@ public:
     virtual void onIdle(double ms) = 0;
 };
 
+}   // namespace sk_app
+
 #endif