Make GM render to render targets that are also textures.

Make GM render to render targets that are also textures.
Committed: https://code.google.com/p/skia/source/detail?r=8438

[bsalomon, 2013-03-28 18:52:10]

The first version of dst-reading effects will only work when the render target
is also a texture. GM currently creates a texture, grabs a ref to its render
target, and then drops the ref to the texture before creating a device. This
means  that the GrTexture object is destroyed and GrRenderTarget::asTexture()
will return NULL.

[robertphillips, 2013-03-28 18:55:50]

lgtm

[bsalomon, 2013-03-28 19:18:21]

Committed patchset #2 manually as r8438 (presubmit successful).