Remove PerformClipping(),CanClipSelf() and the related logic in LTHCommon.

There is a precision lost issue for texture layers with CSS
transforms(Scaling) when applying TextureDrawQuad::PerformClipping()
to avoid explicitly setting a scissor. The rect is first divided by
the scale_factor, then round to integer value and finally multiplied
by the scale_factor in GLRenderer::EnqueueTextureQuad(). The round
process loses precision and the later scale operation enlarges the
error. This error leads to wrong width and height drawn and
introduces visual defects. 

BUG=240259

Review URL: https://codereview.chromium.org/24427006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@227177 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 227177