[startup] Wait until settings are loaded to load locale data

If we want to give users a setting to choose their locale, then we need
to wait until settings are available to load the locale data.

This CL reorders startup so that we load up settings/prefs first.
Also promisify prefs loading so that it's easier to follow ordering
in MainImpl.

Bug: 1167695
Change-Id: I0955e04a0b5f204c8784be2cad7e6b9fa5443b8b
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/2635657
Reviewed-by: Simon Zünd <szuend@chromium.org>
Commit-Queue: Peter Marshall <petermarshall@chromium.org>

front_end/main/MainImpl.js

@@ -84,8 +84,14 @@ export class MainImpl {
     await Root.Runtime.appStarted;
     Root.Runtime.Runtime.setPlatform(Host.Platform.platform());
     Root.Runtime.Runtime.setL10nCallback(ls);
+    const prefs = await new Promise(resolve => {
+      Host.InspectorFrontendHost.InspectorFrontendHostInstance.getPreferences(resolve);
+    });
+
+    console.timeStamp('Main._gotPreferences');
+    this._createSettings(prefs);
     await this.requestAndRegisterLocaleData();
-    Host.InspectorFrontendHost.InspectorFrontendHostInstance.getPreferences(this._gotPreferences.bind(this));
+    this._createAppUI();
   }
 
   async requestAndRegisterLocaleData() {
@@ -101,15 +107,6 @@ export class MainImpl {
     }
   }
 
-  /**
-   * @param {!Object<string, string>} prefs
-   */
-  _gotPreferences(prefs) {
-    console.timeStamp('Main._gotPreferences');
-    this._createSettings(prefs);
-    this._createAppUI();
-  }
-
   /**
    * @param {!Object<string, string>} prefs
    * Note: this function is called from testSettings in Tests.js.