Add openCV dependency to install-build-deps.sh

Context: https://codereview.chromium.org/660893002/

BUG=424345

Review URL: https://codereview.chromium.org/646033009

Cr-Commit-Position: refs/heads/master@{#301404}

build/install-build-deps.sh

@@ -105,7 +105,7 @@ dev_list="apache2.2-bin bison cdbs curl dpkg-dev elfutils devscripts fakeroot
           libpulse-dev libsctp-dev libspeechd-dev libsqlite3-dev libssl-dev
           libudev-dev libwww-perl libxslt1-dev libxss-dev libxt-dev libxtst-dev
           mesa-common-dev openbox patch perl php5-cgi pkg-config python
-          python-cherrypy3 python-crypto python-dev python-openssl
+          python-cherrypy3 python-crypto python-dev python-opencv python-openssl
           python-psutil rpm ruby subversion ttf-dejavu-core ttf-indic-fonts
           ttf-kochi-gothic ttf-kochi-mincho wdiff xfonts-mathml zip
           $chromeos_dev_list"