RenderLayer satellite objects should use references

RenderLayer must have a non-NULL renderer so all the code
can safely be converted to use references. This change
only takes care of the satellite object that RenderLayer
creates. While touching RenderLayerReflectionInfo removed
an unneeded getter and renamed the field to m_box to better
reflect the associated renderer type.

Review URL: https://codereview.chromium.org/247683005

git-svn-id: svn://svn.chromium.org/blink/trunk@172544 bbb929c8-8fbe-4397-9dbb-9b2b20218538
FCMify text-based-repaint layout tests

Repaint tracking happens in both FrameView and GraphicsLayer.  When
layout tests are always composited, then FrameView no longer tracks
repaints and they are all collected on GraphicsLayer.  The
text-based-repaint.js test is adjusted to print out the graphics
layer tree and to force any test using it into FCM.

In order to print out repaint rects, the layer tree has to be printed
out instead.  I looked through all the results and the only differences
are that repaints are now clipped to not extend into negative space and
that repaints are relative to the graphics layer and not the viewport
(so are differently offset by scrolling).

The vast majority of these are text changes, but there are 4 image
changes in svg, that are all using "text"-based-repaint to do pixel
repaint tests.  These are all scrollbar differences similar to
https://codereview.chromium.org/249963002/ and one imperceptible
image scaling change.

A follow up to this would be to remove the FrameView-based repaint
tracking plumbing and only use the GraphicsLayer-based version.

BUG=361729

Review URL: https://codereview.chromium.org/252353002

git-svn-id: svn://svn.chromium.org/blink/trunk@172545 bbb929c8-8fbe-4397-9dbb-9b2b20218538