SkColorSpaceXformer: Add SkShader::makeColorSpace()

SkColorSpaceXformer: Add SkShader::makeColorSpace()

Just a refactor - reimplements the shader xforms with makeColorSpace().

11 gms have diffs.  Some are down to floating precision.  The old
implementation would go float->fixed->float in some cases.  Others
are due to improvements with gradient shaders inside local matrix
shaders.

Bug: skia:6516
Change-Id: I424406990c5c58a47833cf4c9ef146cd3ea6c37e
Reviewed-on: https://skia-review.googlesource.com/13769
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Matt Sarett <msarett@google.com>