refactor gradient stage names

This is just a name refactor and I'm happy to delay it until we're done
with the current wave of gradient CLs.  The main ideas:

  - we use the "linear_gradient" stages for all gradients,
    so cut the "linear" and just call them "gradient";

  - remind ourselves that the 2-stop stage requires even spacing, i.e.
    stops at 0 and 1.  This name should harmonize with Herb's new
    general evenly spaced gradient stage, currently
    "evenly_spaced_linear_gradient", and after it lands and I rebase,
    "evenly_spaced_gradient"

  - remind ourselves which polar coordinate xy_to_polar_unit returns,
    the angle.

Change-Id: I0fd0c8bd4c1ead7d2d0fff45a199d318b71f34ac
Reviewed-on: https://skia-review.googlesource.com/16500
Commit-Queue: Mike Klein <mtklein@chromium.org>
Reviewed-by: Mike Reed <reed@google.com>
diff --git a/src/effects/gradients/SkGradientShader.cpp b/src/effects/gradients/SkGradientShader.cpp
index 6f9b404..042ad45 100644
--- a/src/effects/gradients/SkGradientShader.cpp
+++ b/src/effects/gradients/SkGradientShader.cpp
@@ -380,7 +380,7 @@
             if (!fOrigPos) {
                 // We clamp only when the stops are evenly spaced.
                 // If not, there may be hard stops, and clamping ruins hard stops at 0 and/or 1.
-                // In that case, we must make sure we're using the general linear_gradient stage,
+                // In that case, we must make sure we're using the general "gradient" stage,
                 // which is the only stage that will correctly handle unclamped t.
                 p->append(SkRasterPipeline::clamp_x,  alloc->make<float>(1));
             }
@@ -404,7 +404,7 @@
         f_and_b[0] = SkPM4f::From4f(c_r.to4f() - c_l.to4f());
         f_and_b[1] = c_l;
 
-        p->append(SkRasterPipeline::linear_gradient_2stops, f_and_b);
+        p->append(SkRasterPipeline::evenly_spaced_2_stop_gradient, f_and_b);
     } else {
 
         struct Stop { float t; SkPM4f f, b; };
@@ -493,7 +493,7 @@
             ctx->stops = stopsArray;
         }
 
-        p->append(SkRasterPipeline::linear_gradient, ctx);
+        p->append(SkRasterPipeline::gradient, ctx);
     }
 
     if (!premulGrad && !this->colorsAreOpaque()) {