Handle multiprocess flag in WebView update service.

Instead of letting DevelopmentSettings manage the setting directly and
observing the changes from WebViewUpdateService, have the update service
manage the setting and just expose IPCs for the settings app to use to
get/set the setting. This means we can set a more flexible policy for
whether multiprocess is enabled by default and change it without
touching the settings code, though for now this CL does not change the
behaviour and is just a refactoring.

Bug: 21643067
Test: Toggle multiprocess WebView in developer settings
Change-Id: I3057c09d99f5f6f472a5195a8e14e9164ea5733a
diff --git a/services/core/java/com/android/server/webkit/WebViewUpdateService.java b/services/core/java/com/android/server/webkit/WebViewUpdateService.java
index 0a7454f..311570e 100644
--- a/services/core/java/com/android/server/webkit/WebViewUpdateService.java
+++ b/services/core/java/com/android/server/webkit/WebViewUpdateService.java
@@ -261,6 +261,32 @@
             }
         }
 
+        @Override // Binder call
+        public boolean isMultiProcessEnabled() {
+            return WebViewUpdateService.this.mImpl.isMultiProcessEnabled();
+        }
+
+        @Override // Binder call
+        public void enableMultiProcess(boolean enable) {
+            if (getContext().checkCallingPermission(
+                        android.Manifest.permission.WRITE_SECURE_SETTINGS)
+                    != PackageManager.PERMISSION_GRANTED) {
+                String msg = "Permission Denial: enableMultiProcess() from pid="
+                        + Binder.getCallingPid()
+                        + ", uid=" + Binder.getCallingUid()
+                        + " requires " + android.Manifest.permission.WRITE_SECURE_SETTINGS;
+                Slog.w(TAG, msg);
+                throw new SecurityException(msg);
+            }
+
+            long callingId = Binder.clearCallingIdentity();
+            try {
+                WebViewUpdateService.this.mImpl.enableMultiProcess(enable);
+            } finally {
+                Binder.restoreCallingIdentity(callingId);
+            }
+        }
+
         @Override
         protected void dump(FileDescriptor fd, PrintWriter pw, String[] args) {
             if (getContext().checkCallingOrSelfPermission(android.Manifest.permission.DUMP)