Remove a workaround in gm/xfermodes.cpp

Remove a workaround in gm/xfermodes.cpp

We were performing a deep copy of the pixels in a SkBitmap to work around a bug where drawing an SkBitmap whose pixel memory was set with setPixels to an SkPicture did not preserve the pixel memory.

Since the workaround was written, we have fixed the bug in two ways:
1. If setPixels is called with a pointer, we wrap the pixels in an SkPixelRef.
2. Picture recording now makes a deep copy of mutable bitmaps.

Also switch to using onOnceBeforeDraw, an existing feature on GM that performs the purpose of the init function.

BUG=http://code.google.com/p/skia/issues/detail?id=224

Committed: https://code.google.com/p/skia/source/detail?r=7433

[reed1, 2013-01-28 19:51:58]

Can you say way we're removing it?

[Leon, 2013-01-28 20:22:37]

On 2013/01/28 19:51:58, reed1 wrote:
> Can you say way we're removing it?

New explanation added to the description.

[reed1, 2013-01-28 20:38:05]

lgtm