Store system tracing and continuous tracing in settings.
Store system tracing and continuous tracing in settings.

This will use the settings system to restore system and continuous tracing.
In the case of system, if we have not changed the system setting it will
use the value provided to showSystemTracing. This allows us to auto-enable
system tracing the first time on CrOS.

BUG=214
R=nduca@chromium.org

Review URL: https://codereview.appspot.com/9887043

git-svn-id: 3a56fcae908c7e16d23cb53443ea4795ac387cf2@548 0e6d7f2b-9903-5b78-7403-59d27f066143

bpsinc-native/src_third_party_trace-viewer,bpsinc-native/src_third_party_trace-viewer,bpsinc-native/src_third_party_trace-viewer,bpsinc-native/src_third_party_trace-viewer