[NaCl SDK] nacl_io: add initial sigaction(2) implemenation.

Also, move tests for signal/kill/sigaction to
kernel_proxy_test.cc.

R=binji@chromium.org

Review URL: https://codereview.chromium.org/69933015

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@235146 0039d316-1c4b-4281-b951-d872f2087c98
[Android WebView] Disable flaky AwViewportTest#testInitialScaleClobberQuirk

BUG=319353
TBR=mnaganov@chromium.org

Review URL: https://codereview.chromium.org/72813002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@235147 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 235147