Enable WebViewExtraHeadersSameDomainOnly by default.

Enable this experiment flag by default in preparation for enabling it on
stable via Finch.

Extend the expiry of the related metric so that it keeps collecting data
until after the default-enabling has reached stable.

Bug: 1038002
Change-Id: Ieae23184ab430565df775c1aad4112dc63ae1561
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2477155
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Nate Fischer <ntfschr@chromium.org>
Commit-Queue: Richard Coles <torne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#817692}

android_webview/common/aw_features.cc

@@ -27,7 +27,7 @@ const base::Feature kWebViewDisplayCutout{"WebViewDisplayCutout",
 // occurs. kWebViewExtraHeadersSameOriginOnly is stricter; when that's enabled,
 // this feature has no effect.
 const base::Feature kWebViewExtraHeadersSameDomainOnly{
-    "WebViewExtraHeadersSameDomainOnly", base::FEATURE_DISABLED_BY_DEFAULT};
+    "WebViewExtraHeadersSameDomainOnly", base::FEATURE_ENABLED_BY_DEFAULT};
 
 // Only allow extra headers added via loadUrl() to be sent to the original
 // origin; strip them from the request if a cross-origin redirect occurs.

testing/variations/fieldtrial_testing_config.json

@@ -8056,21 +8056,6 @@
             ]
         }
     ],
-    "WebViewHeaderInjection": [
-        {
-            "platforms": [
-                "android_webview"
-            ],
-            "experiments": [
-                {
-                    "name": "SameDomainOnly",
-                    "enable_features": [
-                        "WebViewExtraHeadersSameDomainOnly"
-                    ]
-                }
-            ]
-        }
-    ],
     "WebViewZeroCopyVideo": [
         {
             "platforms": [

tools/metrics/histograms/histograms_xml/android/histograms.xml

@@ -2369,7 +2369,7 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="Android.WebView.ExtraHeadersRedirect"
-    enum="WebViewExtraHeadersRedirect" expires_after="2020-12-01">
+    enum="WebViewExtraHeadersRedirect" expires_after="2021-02-14">
   <owner>torne@chromium.org</owner>
   <owner>src/android_webview/OWNERS</owner>
   <summary>