Add mark action and reducer

src/content/reducers/mark.js

@@ -0,0 +1,25 @@
+import actions from 'content/actions';
+
+const defaultState = {
+  set: false,
+  jump: false,
+  marks: {},
+};
+
+export default function reducer(state = defaultState, action = {}) {
+  switch (action.type) {
+  case actions.MARK_START_SET:
+    return { ...state, set: true };
+  case actions.MARK_START_JUMP:
+    return { ...state, jump: true };
+  case actions.MARK_CANCEL:
+    return { ...state, set: false, jump: false };
+  case actions.MARK_SET_LOCAL: {
+    let marks = { ...state.marks };
+    marks[action.key] = { y: action.y };
+    return { ...state, marks };
+  }
+  default:
+    return state;
+  }
+}