Adds 'virtual' and 'const' modifiers to methods in wv_cas_ecm.

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Expose header files under export/exported_root/util in media_cas_packager_sdk because util::Status is used in wv_cas_ecm.h

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=218632176

util/error_space.h

@@ -0,0 +1,83 @@
+////////////////////////////////////////////////////////////////////////////////
+// Copyright 2017 Google LLC.
+//
+// This software is licensed under the terms defined in the Widevine Master
+// License Agreement. For a copy of this agreement, please contact
+// widevine-licensing@google.com.
+////////////////////////////////////////////////////////////////////////////////
+
+#ifndef UTIL_ERROR_SPACE_H_
+#define UTIL_ERROR_SPACE_H_
+
+#include <string>
+
+namespace widevine {
+namespace util {
+
+class ErrorSpace {
+ public:
+  std::string SpaceName() const { return space_name_func_(this); }
+  std::string String(int code) const { return code_to_string_func_(this, code); }
+
+ protected:
+  // typedef instead of using statements for SWIG compatibility.
+  typedef std::string (*SpaceNameFunc)(const ErrorSpace* space);
+  typedef std::string (*CodeToStringFunc)(const ErrorSpace* space, int code);
+  constexpr ErrorSpace(SpaceNameFunc space_name_func,
+                       CodeToStringFunc code_to_string_func)
+      : space_name_func_(space_name_func),
+        code_to_string_func_(code_to_string_func) {}
+
+ private:
+  const SpaceNameFunc space_name_func_;
+  const CodeToStringFunc code_to_string_func_;
+};
+
+// Manages creation of error space subclasses.
+template <typename T>
+class ErrorSpaceImpl : public ErrorSpace {
+ public:
+  constexpr ErrorSpaceImpl()
+      : ErrorSpace(&ErrorSpaceImpl::SpaceNameImpl,
+                   &ErrorSpaceImpl::CodeToStringImpl) {}
+
+  // Returns the canonical instance of the `T` error space.
+  static constexpr const T* Get();
+
+ private:
+  // These functions adapt the stateful implementation that takes a space
+  // pointer to stateless static methods, so that clients of ErrorSpaceImpl are
+  // safe to have constexpr global instances.
+  static std::string SpaceNameImpl(const ErrorSpace* /*space*/) {
+    return T::SpaceName();
+  }
+
+  static std::string CodeToStringImpl(const ErrorSpace* /*space*/, int code) {
+    return T::CodeToString(code);
+  }
+};
+
+namespace internal {
+
+// Provides a global constexpr instance of the error space `T`.
+// We need the indirection because ErrorSpaceImpl can't declare constexpr
+// instances of T since it is not yet fully declared.
+template <typename T>
+struct ErrorSpaceInstance {
+  static constexpr T value = {};
+};
+
+template <typename T>
+constexpr T ErrorSpaceInstance<T>::value;
+
+}  // namespace internal
+
+template <typename T>
+constexpr const T* ErrorSpaceImpl<T>::Get() {
+  return &internal::ErrorSpaceInstance<T>::value;
+}
+
+}  // namespace util
+}  // namespace widevine
+
+#endif  // UTIL_ERROR_SPACE_H_