Fix painting glitch with text and NPAPI plugins. This was a regression from r167042. The problem was that for non-transparent windowless plugins we were combining the data below the plugin with the data that the plugin creates. We could just copy directly and not do any alpha-blending.

BUG=164800
Review URL: https://codereview.chromium.org/12487003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@186446 0039d316-1c4b-4281-b951-d872f2087c98
9 files changed