The soft keyboard has arrow buttons for moving the cursor. Theoretically
speaking the buttons should be disabled or have no effect on
ClientKeyboard since hasText returns NO and it doesn't implement
UITextInput, but it seems to still try to call into
[UITextInput selectedTextRange], which crashes the app.

This CL fixes that by implementing the selectedTextRange property to
prevent the app from crashing. The implementation itself does nothing.

Change-Id: I7562d2e6e9ab0b6044ff443bd2b1ededec4223bb
Reviewed-on: https://chromium-review.googlesource.com/608751


Commit-Queue: Yuwei Huang <yuweih@chromium.org>
Reviewed-by: Jamie Walch <jamiewalch@chromium.org>
Cr-Commit-Position: refs/heads/master@{#493626}