API Rename: IC#inputContent to IC#commitContent.

As shown in below, we have already used commit* naming convention in
InputConnection.

 - InputConnection#commitCompletion(CompletionInfo);
 - InputConnection#commitCorrection(CorrectionInfo);
 - InputConnection#commitText(CharSequence, int);

Hence renaming IC#inputContent() to IC#commitContent() would make the
new method more consistent.

Bug: 29450024
Change-Id: Ica1ba3154795c1bf44e140dfe639b299f83cd8af