LibVideo/VP9: Use a struct for block context to keep between frames

There are three fields that we need to store from FrameBlockContext to
keep between frames, which are used to parse for those same fields for
the next frame.

Userland/Libraries/LibVideo/VP9/Context.h

@@ -93,6 +93,39 @@ public:
         return m_storage[index_at(row, column)];
     }
 
+    template<typename OtherT>
+    ErrorOr<void> try_resize_to_match_other_vector2d(Vector2D<OtherT> const& other)
+    {
+        return try_resize(other.height(), other.width());
+    }
+
+    template<typename OtherT, typename Function>
+    void copy_to(Vector2D<OtherT>& other, Function function)
+    {
+        VERIFY(width() <= other.width());
+        VERIFY(height() <= other.height());
+        for (u32 row = 0; row < height(); row++) {
+            for (u32 column = 0; column < width(); column++)
+                other.at(row, column) = function(at(row, column));
+        }
+    }
+
+    void copy_to(Vector2D<T>& other)
+    {
+        VERIFY(width() <= other.width());
+        VERIFY(height() <= other.height());
+        for (u32 row = 0; row < height(); row++) {
+            auto other_index = other.index_at(row, 0);
+            AK::TypedTransfer<T>::copy(&m_storage[index_at(row, 0)], &other[other_index], width());
+        }
+    }
+
+    void reset()
+    {
+        for (size_t i = 0; i < size(); i++)
+            m_storage[i] = T();
+    }
+
 private:
     u32 m_height { 0 };
     u32 m_width { 0 };
@@ -124,4 +157,25 @@ struct FrameBlockContext {
     u8 segment_id { 0 };
 };
 
+// Block context that is kept between frames until explictly cleared.
+struct PersistentBlockContext {
+    PersistentBlockContext()
+        : available(false)
+    {
+    }
+
+    PersistentBlockContext(FrameBlockContext const& frame_context)
+        : available(frame_context.is_available)
+        , ref_frames(frame_context.ref_frames)
+        , primary_motion_vector_pair(frame_context.primary_motion_vector_pair())
+        , segment_id(frame_context.segment_id)
+    {
+    }
+
+    bool available { false };
+    ReferenceFramePair ref_frames { ReferenceFrameType::None, ReferenceFrameType::None };
+    MotionVectorPair primary_motion_vector_pair {};
+    u8 segment_id { 0 };
+};
+
 }