android: Add systrace and combined trace support to adb_profile_chrome

This patch adds systrace support to adb_profile_chrome. You can either
either capture a standalone systrace or a combined Chrome + systrace
which includes data from both sources.

The advantages of a combined trace compared to a normal systrace with
the 'webview' category are:

 - Support for advanced Chrome trace features such as object dumps
   (e.g., --trace-cc and --trace-gpu), instant events ('X') and flow
   events.
 - Reduced tracing overhead since Chrome trace events do not need to
   make the trip through the kernel trace marker file.

Note that viewing combined traces requires some further work in Trace
Viewer to properly align the clocks from different event streams.

This patch also removes the standalone --start, --stop and --download
options from the script because they are of dubious value and supporting
them with systrace is not straightforward.

BUG=294883

Review URL: https://codereview.chromium.org/25686006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228669 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228669
policy: Remove ConfigurationPolicyHandlerList from DEPS exceptions.

This class will stay in chrome/browser/policy.

BUG=271392

Review URL: https://codereview.chromium.org/25539005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228670 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228670