base

Browse mode for DocumentsUI, removed volume state.

The existing management mode is too specific, and requires that
storage backends add queryChildDocumentsForManage(), etc.  Instead,
to offer more natural browsing support, add a new BROWSE_ROOT intent.

It behaves mostly like MANAGE_ROOT, except that it doesn't mutate
its Uris with setManageMode(), and it shortcuts straight to VIEW on
clicked documents.

It can be launched like this:

$ adb shell am start -a android.provider.action.BROWSE_ROOT
    -d content://com.android.externalstorage.documents/root/8405-1DFB
    -c android.intent.category.DEFAULT

Also rename a MetricsConstants to make it clearer, and don't
auto-mount all emulated volumes.

Fix bugs around parceling of DiskInfo/VolumeInfo.  Method to resolve
the best description for a VolumeInfo, which might need to fall
back to DiskInfo.

Add back "removed" volume state so we send broadcast when a volume
is destroyed, matching the expected public API behavior.

Bug: 19993667
Change-Id: I13aff32c5e11dfc63da44aee9e93a27f4690a43f