[NaCl SDK Docs] redirect chromesite root to index instead of overview

Also some chrome_sidenav changes.

BUG=none
R=sbc@chromium.org

Review URL: https://codereview.chromium.org/183703004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@254630 0039d316-1c4b-4281-b951-d872f2087c98
Part 7 of search provider refactoring.

Move ParseSuggestResults into superclass and call it from both
subclasses.
Introduces several helpers methods to introduce seams for zero
suggest's input handling.

BUG=338955
TBR=mpearson

Review URL: https://codereview.chromium.org/174513002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@254631 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 254630
SVN changes up to revision 254631