Layers: Add code-gen'd calls to val exts

Modified PV code gen to insert and make calls to validate
extension dependencies.

Change-Id: I90103b16d36fb868b32df796b1dae7741dfcba34
diff --git a/layers/parameter_validation_utils.h b/layers/parameter_validation_utils.h
index d5497cb..791a7a1 100644
--- a/layers/parameter_validation_utils.h
+++ b/layers/parameter_validation_utils.h
@@ -86,6 +86,9 @@
 // The value of all VK_xxx_MAX_ENUM tokens
 const uint32_t MaxEnumValue = 0x7FFFFFFF;
 
+// Forward declaration
+bool ValidateRequiredExtensions(std::string api_name, const std::vector<std::string> required_extensions);
+
 template <typename T>
 bool is_extension_added_token(T value) {
     return (value != MaxEnumValue) && (static_cast<uint32_t>(std::abs(static_cast<int32_t>(value))) >= ExtEnumBaseValue);