Mixed Content: Add use counters for content types.

Mixed Content: Add use counters for content types.

This patch adds 'MixedContentPresent' to get a feel for the number of
pages which attempt to load mixed content, 'MixedContentBlockable' to
measure the subset which is blocked outright, and 'MixedContent*' to
count the individual types we don't yet block. Over time, the goal is
to bring the latter counters down to zero by moving content types into
the 'Blockable' category.

BUG=388650
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=186794

[Mike West, 2014-12-09 09:20:21]

mkwst@chromium.org changed reviewers:
+ jochen@chromium.org

[Mike West, 2014-12-09 09:20:21]

WDYT, Jochen?

jschuh: FYI.

[jochen (gone - plz use gerrit), 2014-12-09 15:57:11]

lgtm

[Mike West, 2014-12-09 18:18:21]

The CQ bit was checked by mkwst@chromium.org

[commit-bot: I haz the power, 2014-12-09 18:18:42]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/785133004/1

[commit-bot: I haz the power, 2014-12-09 18:29:57]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=186794