LeakExpectations: fix the duplicated entry callstack-placards-discarded.html

The leak detector bots is red because of the duplicated entry (http://build.chromium.org/p/chromium.webkit/builders/WebKit%20Linux%20Leak/builds/1279).

NOTRY=true
BUG=376188, 364408, 371264
R=kouhei@chromium.org

Review URL: https://codereview.chromium.org/296903008

git-svn-id: svn://svn.chromium.org/blink/trunk@174672 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Get rid of HashMap deleteAllKeys/deleteAllValues functions

Get rid of HashMap deleteAllKeys/deleteAllValues
functions as:
1) They are almost never used.
2) Using of those is not adviseable as they leave
   the container with the deleted pointers inside.
   OwnPtrs should be used instead.

Review URL: https://codereview.chromium.org/296513019

git-svn-id: svn://svn.chromium.org/blink/trunk@174673 bbb929c8-8fbe-4397-9dbb-9b2b20218538