[CSS Blending] background-blend-mode fails for certain SVG files.
Porting webkit fix from https://bugs.webkit.org/show_bug.cgi?id=127350:
The graphics context of the SVG inherits the blend mode set on the
background layer. Fix consists in drawing the SVG in a transparency
layer.

BUG=229166

Review URL: https://codereview.chromium.org/145063003

git-svn-id: svn://svn.chromium.org/blink/trunk@165628 bbb929c8-8fbe-4397-9dbb-9b2b20218538