aw: Enable WebViewPageStartedOnCommit by default

Enabled by experiment until now. Have not heard many bugs. Time to
eanble by default for 74 (and remove the switch later).

Bug: 896022
Change-Id: I975f1f91c6c80404e6debc369b1a9ca9cdf45455
Reviewed-on: https://chromium-review.googlesource.com/c/1489106Reviewed-by: Richard Coles <torne@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Commit-Queue: Bo <boliu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#635719}

android_webview/browser/aw_feature_list.cc

@@ -51,7 +51,7 @@ const base::Feature kWebViewConnectionlessSafeBrowsing{
 // Kill switch for feature to call onPageFinished for browser-initiated
 // navigations when the navigation commits.
 const base::Feature kWebViewPageStartedOnCommit{
-    "WebViewPageStartedOnCommit", base::FEATURE_DISABLED_BY_DEFAULT};
+    "WebViewPageStartedOnCommit", base::FEATURE_ENABLED_BY_DEFAULT};
 
 // Whether the application package name is logged in UMA.
 const base::Feature kWebViewUmaLogAppPackageName{

testing/variations/fieldtrial_testing_config.json

@@ -472,21 +472,6 @@
             ]
         }
     ],
-    "AndroidWebViewPageStartedOnCommit": [
-        {
-            "platforms": [
-                "android_webview"
-            ],
-            "experiments": [
-                {
-                    "name": "Enabled",
-                    "enable_features": [
-                        "WebViewPageStartedOnCommit"
-                    ]
-                }
-            ]
-        }
-    ],
     "AppLauncherRefresh": [
         {
             "platforms": [