Merge 32311 - Hold histograms in static variables instead of allocating heap....

Merge 32311 - Hold histograms in static variables instead of allocating heap.

If instance variables holding pointers to Histograms, it would cause
crash bug when the instance is torn down and the metrics services use
and recording of their contents.

The current "standard" patten for using Histograms includes making sure
that the Histogram instances are not destroyed prematurely, held in
static variables.

BUG=28096
TEST=none

Review URL: http://codereview.chromium.org/404022

TBR=ukai@chromium.org

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=33185