Fix crash when resizing a view destroys the render tree

This is a simple fix for not holding a renderer across FrameView
resizes. Calling view->resize() can destroy renderers so this patch
updates SVGImage::setContainerSize to query the renderer after the
resize is complete. A similar issue does not exist for the dom tree
which is not destroyed.

BUG=344492

Review URL: https://codereview.chromium.org/178043006

git-svn-id: svn://svn.chromium.org/blink/trunk@168113 bbb929c8-8fbe-4397-9dbb-9b2b20218538