Fix crashing in FFmpegGlueTest.Write and friends
Fix crashing in FFmpegGlueTest.Write and friends

BUG=36037
TEST=FFmpegGlueTest.* runs on build bot

FFmpegGlueTest.Write was crashing on build bots due to that it
has dependencies on previous test to run. And strangely the build bot
didn't run all the test cases, resulting the crash.

This is fixed by extracting the initialization step and putting it
into a common test setup task.

Review URL: http://codereview.chromium.org/668034

git-svn-id: http://src.chromium.org/svn/trunk/src@40800 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 4e164419517a3f23e9a35d64e3a1c092cb770733
meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser