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diff --git a/devtools/shared/async-storage.js b/devtools/shared/async-storage.js
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+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/**
+ *
+ * Adapted from https://github.com/mozilla-b2g/gaia/blob/f09993563fb5fec4393eb71816ce76cb00463190/shared/js/async_storage.js
+ * (converted to use Promises instead of callbacks).
+ *
+ * This file defines an asynchronous version of the localStorage API, backed by
+ * an IndexedDB database.  It creates a global asyncStorage object that has
+ * methods like the localStorage object.
+ *
+ * To store a value use setItem:
+ *
+ *   asyncStorage.setItem("key", "value");
+ *
+ * This returns a promise in case you want confirmation that the value has been stored.
+ *
+ *  asyncStorage.setItem("key", "newvalue").then(function() {
+ *    console.log("new value stored");
+ *  });
+ *
+ * To read a value, call getItem(), but note that you must wait for a promise
+ * resolution for the value to be retrieved.
+ *
+ *  asyncStorage.getItem("key").then(function(value) {
+ *    console.log("The value of key is:", value);
+ *  });
+ *
+ * Note that unlike localStorage, asyncStorage does not allow you to store and
+ * retrieve values by setting and querying properties directly. You cannot just
+ * write asyncStorage.key; you have to explicitly call setItem() or getItem().
+ *
+ * removeItem(), clear(), length(), and key() are like the same-named methods of
+ * localStorage, and all return a promise.
+ *
+ * The asynchronous nature of getItem() makes it tricky to retrieve multiple
+ * values. But unlike localStorage, asyncStorage does not require the values you
+ * store to be strings.  So if you need to save multiple values and want to
+ * retrieve them together, in a single asynchronous operation, just group the
+ * values into a single object. The properties of this object may not include
+ * DOM elements, but they may include things like Blobs and typed arrays.
+ *
+ */
+
+"use strict";
+
+const DBNAME = "devtools-async-storage";
+const DBVERSION = 1;
+const STORENAME = "keyvaluepairs";
+var db = null;
+
+function withStore(type, onsuccess, onerror) {
+  if (db) {
+    const transaction = db.transaction(STORENAME, type);
+    const store = transaction.objectStore(STORENAME);
+    onsuccess(store);
+  } else {
+    const openreq = indexedDB.open(DBNAME, DBVERSION);
+    openreq.onerror = function withStoreOnError() {
+      onerror();
+    };
+    openreq.onupgradeneeded = function withStoreOnUpgradeNeeded() {
+      // First time setup: create an empty object store
+      openreq.result.createObjectStore(STORENAME);
+    };
+    openreq.onsuccess = function withStoreOnSuccess() {
+      db = openreq.result;
+      const transaction = db.transaction(STORENAME, type);
+      const store = transaction.objectStore(STORENAME);
+      onsuccess(store);
+    };
+  }
+}
+
+function getItem(itemKey) {
+  return new Promise((resolve, reject) => {
+    let req;
+    withStore(
+      "readonly",
+      store => {
+        store.transaction.oncomplete = function onComplete() {
+          let value = req.result;
+          if (value === undefined) {
+            value = null;
+          }
+          resolve(value);
+        };
+        req = store.get(itemKey);
+        req.onerror = function getItemOnError() {
+          console.error("Error in asyncStorage.getItem():", req.error.name);
+          reject(req.error);
+        };
+      },
+      reject
+    );
+  });
+}
+
+function setItem(itemKey, value) {
+  return new Promise((resolve, reject) => {
+    withStore(
+      "readwrite",
+      store => {
+        store.transaction.oncomplete = resolve;
+        const req = store.put(value, itemKey);
+        req.onerror = function setItemOnError() {
+          console.error("Error in asyncStorage.setItem():", req.error.name);
+          reject(req.error);
+        };
+      },
+      reject
+    );
+  });
+}
+
+function removeItem(itemKey) {
+  return new Promise((resolve, reject) => {
+    withStore(
+      "readwrite",
+      store => {
+        store.transaction.oncomplete = resolve;
+        const req = store.delete(itemKey);
+        req.onerror = function removeItemOnError() {
+          console.error("Error in asyncStorage.removeItem():", req.error.name);
+          reject(req.error);
+        };
+      },
+      reject
+    );
+  });
+}
+
+function clear() {
+  return new Promise((resolve, reject) => {
+    withStore(
+      "readwrite",
+      store => {
+        store.transaction.oncomplete = resolve;
+        const req = store.clear();
+        req.onerror = function clearOnError() {
+          console.error("Error in asyncStorage.clear():", req.error.name);
+          reject(req.error);
+        };
+      },
+      reject
+    );
+  });
+}
+
+function length() {
+  return new Promise((resolve, reject) => {
+    let req;
+    withStore(
+      "readonly",
+      store => {
+        store.transaction.oncomplete = function onComplete() {
+          resolve(req.result);
+        };
+        req = store.count();
+        req.onerror = function lengthOnError() {
+          console.error("Error in asyncStorage.length():", req.error.name);
+          reject(req.error.name);
+        };
+      },
+      reject
+    );
+  });
+}
+
+function key(n) {
+  return new Promise((resolve, reject) => {
+    if (n < 0) {
+      resolve(null);
+      return;
+    }
+
+    let req;
+    withStore(
+      "readonly",
+      store => {
+        store.transaction.oncomplete = function onComplete() {
+          const cursor = req.result;
+          resolve(cursor ? cursor.key : null);
+        };
+        let advanced = false;
+        req = store.openCursor();
+        req.onsuccess = function keyOnSuccess() {
+          const cursor = req.result;
+          if (!cursor) {
+            // this means there weren"t enough keys
+            return;
+          }
+          if (n === 0 || advanced) {
+            // Either 1) we have the first key, return it if that's what they
+            // wanted, or 2) we"ve got the nth key.
+            return;
+          }
+
+          // Otherwise, ask the cursor to skip ahead n records
+          advanced = true;
+          cursor.advance(n);
+        };
+        req.onerror = function keyOnError() {
+          console.error("Error in asyncStorage.key():", req.error.name);
+          reject(req.error);
+        };
+      },
+      reject
+    );
+  });
+}
+
+exports.getItem = getItem;
+exports.setItem = setItem;
+exports.removeItem = removeItem;
+exports.clear = clear;
+exports.length = length;
+exports.key = key;