Dismiss "Add to dictionary" hint with non-special char event

This CL slightly extends the condition when "Add to dictionary"
hint is dismissed.

With this CL, "Add to dictionary hint" will be dismissed by any
non-special char event. This is more comfortable especially if
we start using more intrusive UIs such as indicator and/or
background color with the text hint in the suggestion strip.

Change-Id: I2ea0fa40d9c6663ebf5d5439be3eca2a2cbd5166