Add a setting to allow window object reuse across a top-level initial navigation.

third_party/WebKit/Source/core/frame/Settings.in

 # Defines properties which are available on the Settings object.
 #
 # Please think carefully before adding a new Setting.  Some questions to
 # consider are:
 # - Should this be a RuntimeEnabledFeature instead? Settings are for things
 #   which we support either values of at runtime.  Features are set at renderer
 #   process startup and are never changed. Features also tend to be set to a
 #   value based on the platform or the stability of the code in question, where
 #   as settings both codepaths need to be stable.
 # - How will you ensure test coverage of all relevant values of your setting?
@@ skipping 196 matching lines @@
 mainFrameClipsContent initial=true
 
 # For android.webkit.WebSettings.setUseWideViewport()
 # http://developer.android.com/reference/android/webkit/WebSettings.html#setUseWideViewPort(boolean)
 useWideViewport initial=true, invalidate=ViewportDescription
 
 # For android.webkit.WebSettings.setLoadWithOverviewMode()
 # http://developer.android.com/reference/android/webkit/WebSettings.html#setLoadWithOverviewMode(boolean)
 loadWithOverviewMode initial=true, invalidate=ViewportDescription
 
+# Used by android_webview to support legacy apps that inject script into a top-level initial empty
+# document and expect it to persist on navigation, even though the origin is unique. Note that this
+# behavior violates the requirements described by [Initialising a new Document object] in
+# https://html.spec.whatwg.org/multipage/browsers.html#navigating-across-documents.
+shouldReuseGlobalForUnownedMainFrame initial=false
+
 ######## End of settings used by Android WebView ########
 
 
 # Touch based text selection and editing on desktop.
 # crbug.com/304873 tracks removal once it's been enabled on all platforms.
 touchEditingEnabled initial=false
 
 # Settings for experimental desktop pinch-zoom support (with semantics
 # optimized for large screens).  Pinch-zoom generally is implemented mainly
 # outside of blink (in the compositor) and doesn't require any settings.
@@ skipping 157 matching lines @@
 # The autoplay gesture override experiment is described in crbug.com/487345 .
 autoplayExperimentMode type=String, initial="off"
 
 # When DevTools is emulating mobile device, frame resize may mean device size has changed,
 # which in turn affects media queries.
 resizeIsDeviceSizeChange initial=false
 
 # Whether the browser process sends gesture events for wheel events.
 # Can be removed when crbug.com/598798 is fixed.
 wheelGesturesEnabled initial=false