Enable new style launcher by default

1. Fix test error ArcAppModelBuilderTest.IconLoadNonSupportedScales
   which is caused by icon file path not found. 64px icon is supported
   by CL http://go/cgcl/1154136. Test fails because the icon size with
   2.0 scale factor, namely 128px, cannot be found, so add those icons.
2. Enable feature flag by default.

Bug: 871444
Change-Id: I9f54f71cfb8cf2fbd73dcb2f9b7da514a231ad0f
Reviewed-on: https://chromium-review.googlesource.com/1164243
Commit-Queue: Weidong Guo <weidongg@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#581140}

ash/public/cpp/app_list/app_list_features.cc

@@ -26,7 +26,7 @@ const base::Feature kEnableSettingsShortcutSearch{
 const base::Feature kEnableAppsGridGapFeature{"EnableAppsGridGapFeature",
                                               base::FEATURE_ENABLED_BY_DEFAULT};
 const base::Feature kEnableNewStyleLauncher{"EnableNewStyleLauncher",
-                                            base::FEATURE_DISABLED_BY_DEFAULT};
+                                            base::FEATURE_ENABLED_BY_DEFAULT};
 const base::Feature kEnableContinueReading{"EnableContinueReading",
                                            base::FEATURE_DISABLED_BY_DEFAULT};
 const base::Feature kEnableZeroStateSuggestions{