Iteration on multi-user external storage.

Remove single-user bind mounts, since they need to remain as raw
mounts to correctly propagate when remounted.  This means we're back
to using sdcard_r GID to enforce READ_EXTERNAL_STORAGE.

Bug: 6925012
Change-Id: I41b5d7ddc985a5df2e288632a0a80d4724089e00

Author: jsharkey

core/java/android/os/Process.java

@@ -582,9 +582,7 @@ private static ProcessStartResult startViaZygote(final String processClass,
             if ((debugFlags & Zygote.DEBUG_ENABLE_ASSERT) != 0) {
                 argsForZygote.add("--enable-assert");
             }
-            if (mountExternal == Zygote.MOUNT_EXTERNAL_SINGLEUSER) {
-                argsForZygote.add("--mount-external-singleuser");
-            } else if (mountExternal == Zygote.MOUNT_EXTERNAL_MULTIUSER) {
+            if (mountExternal == Zygote.MOUNT_EXTERNAL_MULTIUSER) {
                 argsForZygote.add("--mount-external-multiuser");
             }
             argsForZygote.add("--target-sdk-version=" + targetSdkVersion);

core/java/com/android/internal/os/ZygoteConnection.java

@@ -527,8 +527,6 @@ private void parseArgs(String args[])
                                 "Duplicate arg specified");
                     }
                     niceName = arg.substring(arg.indexOf('=') + 1);
-                } else if (arg.equals("--mount-external-singleuser")) {
-                    mountExternal = Zygote.MOUNT_EXTERNAL_SINGLEUSER;
                 } else if (arg.equals("--mount-external-multiuser")) {
                     mountExternal = Zygote.MOUNT_EXTERNAL_MULTIUSER;
                 } else {

services/java/com/android/server/am/ActivityManagerService.java

@@ -1982,18 +1982,13 @@ private final void startProcessLocked(ProcessRecord app,
                 try {
                     final PackageManager pm = mContext.getPackageManager();
                     gids = pm.getPackageGids(app.info.packageName);
-                    if (pm.checkPermission(
-                            android.Manifest.permission.READ_EXTERNAL_STORAGE, app.info.packageName)
-                            == PERMISSION_GRANTED) {
-                        if (Environment.isExternalStorageEmulated()) {
-                            mountExternal = Zygote.MOUNT_EXTERNAL_MULTIUSER;
-                        } else {
-                            mountExternal = Zygote.MOUNT_EXTERNAL_SINGLEUSER;
-                        }
-                    }
                 } catch (PackageManager.NameNotFoundException e) {
                     Slog.w(TAG, "Unable to retrieve gids", e);
                 }
+
+                if (Environment.isExternalStorageEmulated()) {
+                    mountExternal = Zygote.MOUNT_EXTERNAL_MULTIUSER;
+                }
             }
             if (mFactoryTest != SystemServer.FACTORY_TEST_OFF) {
                 if (mFactoryTest == SystemServer.FACTORY_TEST_LOW_LEVEL