Re-Reland: [Telemetry] Properly handle retries after browser crash.

Previously it was easy for the results to get into a bad state and assert in a
variety of ways.

This ensures we ignore the partial results in the case of a crash.

This reland is tested with GPU functional tests. The main fix was to make all
result types shallow copyable.

BUG=
TBR=tonyg@chromium.org

Review URL: https://codereview.chromium.org/147853002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247184 0039d316-1c4b-4281-b951-d872f2087c98
Mount "Downloads" directory to different mount point name for each profile.

This enables cross-profile file copying among "Downloads" folders of Files.app.

BUG=336090

Review URL: https://codereview.chromium.org/143013002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247185 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 247184
SVN changes up to revision 247185