Revert "Base Gradient FP Refactor"

This reverts commit 10f7a1e07554a362aef979d32ba288a009bdff90.

Reason for revert: broke google3 roll
Original change's description:
> Base Gradient FP Refactor
> 
> --
> 
> Redefines how gradients will be written in the GPU back-end:
> 
> They are split into three fragment processor components: master, layout, and colorizer.
> The layout FP is responsible for converting the fragment position into an interpolant value, t.
> Each high-level gradient--such as linear, radial, etc.--are implemented solely in a layout FP.
> The colorizer FP is responsible for converting t into a color.
> The master FP invokes the layout, clamps t into the proper domain, and then invokes the colorizer.
> GrGradientShader provides factory functions to create FP graphs from SkGradientShader instances.
> This pattern is documented in gpu/gradients/README.md.
> 
> Goals for current CL
> ====================
> 
> Outline the FP components by providing .fp implementations for the simplest gradients.
> Defines a two-color single interval colorizer and a linear gradient layout, and the master effect.
> A MakeLinear() factory function is provided that can convert SkGradientShaders that fit these constraints.
> SkLinearGradient first attempts to use the new system, falling back to the original GrGradientEffect.
> 
> Future CLs
> ==========
> 
> To keep the CL reviews manageable, additional dependent CLs will be added that gradually replace past functionality.
> A CL for each layout will be defined.
> CLs for the different analytic colorizer cases and the textured gradient case will be defined.
> Once the new system supports all current layouts and colorizer capabilities, all old GPU gradient code will be removed.
> After this clean-up, analytic colorization can hopefully be expanded to reduce the usage of textured gradients.
> 
> Bug: skia:
> Change-Id: Iafe7b8b4071491a71c473babcd7bedda659150c1
> Reviewed-on: https://skia-review.googlesource.com/148120
> Commit-Queue: Michael Ludwig <michaelludwig@google.com>
> Reviewed-by: Brian Salomon <bsalomon@google.com>

TBR=bsalomon@google.com,michaelludwig@google.com

Change-Id: Ib735e323795ac8874cb00b007a915786b50517a6
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: skia:
Reviewed-on: https://skia-review.googlesource.com/153600
Reviewed-by: Cary Clark <caryclark@google.com>
Commit-Queue: Cary Clark <caryclark@google.com>
23 files changed