add find action and reducer

src/content/actions/find.js

@@ -0,0 +1,36 @@
+//
+// window.find(aString, aCaseSensitive, aBackwards, aWrapAround,
+//             aWholeWord, aSearchInFrames, aShowDialog);
+//
+// NOTE: window.find is not standard API
+// https://developer.mozilla.org/en-US/docs/Web/API/Window/find
+
+import actions from 'content/actions';
+
+const show = () => {
+  return { type: actions.FIND_SHOW };
+};
+
+const hide = () => {
+  return { type: actions.FIND_HIDE };
+};
+
+const next = (keyword) => {
+  // TODO Error on no matched
+  window.find(keyword, false, false, true, false, true, false);
+  return {
+    type: actions.FIND_SET_KEYWORD,
+    keyword,
+  };
+};
+
+const prev = (keyword) => {
+  // TODO Error on no matched
+  window.find(keyword, false, true, true, false, true, false);
+  return {
+    type: actions.FIND_SET_KEYWORD,
+    keyword,
+  };
+};
+
+export { show, hide, next, prev };