[Android] Cherry-pick r278950 (0e40ce9) from upstream

Author: mnaganov@chromium.org

Disable ChildTraceMessageFilter in single process mode

This fixes chrome://inspect traces for Android WebView.

ChildTraceMessageFilter instances are all talking to the same TraceLog
instance and confuse it. Enabling tracing in browser is enough, since
everyone lives in the same process.

Review URL: https://codereview.chromium.org/349633003

BUG=XWALK-1571
Merge pull request #175 from kurli/crosswalk-7-fix-tracing

[Android] Cherry-pick r278950 (0e40ce9) from upstream