[SVG] Incorrect large filter clamping transformation.

RenderSVGResourceFilter::applyResource() performs ImageBuffer size 
clamping before calling createImageBuffer (by adjusting its 
scale/effective transform). This clashes with the existing
createImageBuffer() clamping logic and results in an incorrect
ImageBuffer context CTM.

Since RenderSVGResourceFilter is the only createImageBuffer client, we
can relocate the method and remove the extra clamping.

Test: svg/filters/filter-huge-clamping.svg

BUG=161624
R=pdr@chromium.org,schenney@chromium.org

Review URL: https://chromiumcodereview.appspot.com/23480062

git-svn-id: svn://svn.chromium.org/blink/trunk@157544 bbb929c8-8fbe-4397-9dbb-9b2b20218538