Pepper: Change ResourceMessageTestSink API for getting multiple messages.
- Remove GetNext* methods.
- Add GetAll* methods, returning a vector of Params/Msg pairs.

BUG=

Review URL: https://codereview.chromium.org/127243002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@243907 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 243907