Revert "Let WebViewImpl::textInputInfo() query the focused element when selection is empty"

This reverts commit 31ed7f3d8e05fce9f3fcc56e9b3de3f4d34f43e8.

It broke contentshell_instrumentation_tests on Android, in particular:
org.chromium.content.browser.input.ImeTest#testImeSelectAndUnSelectAll

BUG=318460
TBR=abarth@chromium.org,b.keleman@samsung.com

Review URL: https://codereview.chromium.org/113063004

git-svn-id: svn://svn.chromium.org/blink/trunk@163732 bbb929c8-8fbe-4397-9dbb-9b2b20218538