Fix & cleanup Renderer4 histograms.
Fix & cleanup Renderer4 histograms.

Changes:
  1) I fixed a bug where we recorded the wrong value for BeginToFinish
     histograms.
  2) Because of (1), it means we need to rename "Renderer4" to something
     else (so that we don't mix the old wrong values with the new right
     ones).  I decided to rename to "PLT", because it is more accurate.
  3) DumpLoadHistograms() is long and the order was a bit confused.
  4) There were instances where we used different histogram ranges for
     a few (possibly legacy?) histograms.  Made all of them uses a
     common format.

Overall, it's not very different than the original version, except it will
look like a huge diff.  I hope it is more readable now.

BUG=none
TEST=none

Review URL: http://codereview.chromium.org/2749016

git-svn-id: http://src.chromium.org/svn/trunk/src@49564 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 3d79b627e1768f286838c8db4b7aff64ae94b47f
meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser