Decode images to sRGB, premultiply based on framework define

This reenables color conversion to sRGB at decode time.

Use the value ANDROID_LINEAR_BLENDING_ENABLED to decide
whether to use the codec's linear premultiply or manually
perform a legacy premultiply.

Test: Demonstrated that legacy premultiply is still
faster than the linear premultiply.  So the performance
of the two pass approach (decode, then premultiply)
is acceptable.  Skia tests both of these decoding modes.

BUG:33741991
BUG:8860389
BUG:24279600

Change-Id: Idea0f359565bd8c7c3ba06e77a897173677db1c6