Simplify code for configuring suppression of ImageDecoder warnings

For images.png.suppressDecoderWarnings and
images.jpeg.suppressDecoderWarnings, the default behavior is now:

	Debug - DON'T suppress
	Developer Release - suppress
	Release - suppress

This behavior can be changed in Debug and in Developer through
the SkRTConf mechanism.

BUG=skia:1680
R=caryclark@google.com

Review URL: https://codereview.chromium.org/26863003

git-svn-id: http://skia.googlecode.com/svn/trunk@11749 2bbb7eff-a529-9590-31e7-b0007b416f81
2 files changed