Provide command to change WebView implementation.

Add a shell command for switching webview implementation so that this
can be done automatically - without interacting with a Dev Setting.

Bug: 27540566
Change-Id: I3c4acaa1b8f4ba24c637ef8a1d48cc7b2616bd91
diff --git a/services/core/java/com/android/server/webkit/WebViewUpdateService.java b/services/core/java/com/android/server/webkit/WebViewUpdateService.java
index a54c542..4669676 100644
--- a/services/core/java/com/android/server/webkit/WebViewUpdateService.java
+++ b/services/core/java/com/android/server/webkit/WebViewUpdateService.java
@@ -613,7 +613,12 @@
                 throw new SecurityException(msg);
             }
 
-            return WebViewUpdateService.this.changeProviderAndSetting(newProvider);
+            long callingId = Binder.clearCallingIdentity();
+            try {
+                return WebViewUpdateService.this.changeProviderAndSetting(newProvider);
+            } finally {
+                Binder.restoreCallingIdentity(callingId);
+            }
         }
 
         @Override // Binder call