Make SVGImage::nativeImageForCurrentFrame draw with a container size

      SVGImage::nativeImageForCurrentFrame() should return an SVG image
rendered as a bitmap at the native size. Before this patch, the image
would not be correctly laid out due to a missing setContainerSize
found in drawImageForContainer(...) but not draw(...). This patch
switches to using the container draw routine.

The test for this patch is a manual test: load the testcase in
http://crbug.com/263087 and verify that the SVG image drags at the
correct resolution.

BUG=263087

Review URL: https://chromiumcodereview.appspot.com/21004002

git-svn-id: svn://svn.chromium.org/blink/trunk@155107 bbb929c8-8fbe-4397-9dbb-9b2b20218538