Move Android TraceEvent interface to base

The platform independent C++ code for TraceEvent has always been in base.
This CL moves the Android specific code into base to match.

This CL is needed now since trace is used by the Android library loader,
which is moving out of content.

Review URL: https://codereview.chromium.org/131553003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@244153 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 244153