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This CL fixes some typos, broken links and other small issues in extension docs. 

Thanks for Sunny Jerry (ratsunny@gmail.com). Some of these mistakes were discovered by him and listed at https://code.google.com/p/chrome-documentation-chs/source/browse/documentation/error_list.txt .

BUG=173630,168952,119535,167355
TEST=none

Review URL: https://chromiumcodereview.appspot.com/12223068

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@182168 0039d316-1c4b-4281-b951-d872f2087c98