Revert of Add SkBitmap::readPixels() and reimplement copyTo and SkCanvas::readPixels

Revert of Add SkBitmap::readPixels() and reimplement copyTo and SkCanvas::readPixels (https://codereview.chromium.org/388803007/)

Reason for revert:
still failing (randomly?) bench sometimes. need stack dump to diagnose.

Original issue's description:
> Add SkBitmap::readPixels() and reimplement copyTo and SkCanvas::readPixels
> usning it.
> 
> Revert "Revert of add readPixels() to SkBitmap (https://codereview.chromium.org/377303002/)"
> 
> This reverts commit d08cb905a7cc80d8fb868bbd14fffe1cd68adcce.
> 
> TBR=scroggo@google.com
> 
> Committed: https://skia.googlesource.com/skia/+/debba5c3d091159149f8a88ab5dcd44dd72e0dc7

TBR=reed@google.com
NOTREECHECKS=true
NOTRY=true

Committed: https://skia.googlesource.com/skia/+/651eaeadeb0b1407f5fe192aeda90db1680fa2b8

[reed2, 2014-07-12 20:15:02]

Created Revert of Add SkBitmap::readPixels() and reimplement copyTo and
SkCanvas::readPixels

[commit-bot: I haz the power, 2014-07-12 20:16:04]

CQ is trying da patch. Follow status at
 https://skia-tree-status.appspot.com/cq/reed@chromium.org/382543005/1

[commit-bot: I haz the power, 2014-07-12 20:16:15]

Change committed as 651eaeadeb0b1407f5fe192aeda90db1680fa2b8

[reed2, 2014-07-13 10:59:35]

A revert of this CL has been created in
https://codereview.chromium.org/392453002/ by reed@chromium.org.

The reason for reverting is: found and fixed the asserts -- we were drawing with
unpremul bitmaps, but our blits assumed they were premul. Fix was to detect this
and just draw nothing..