Revert of Add gpu implementation of OverdrawXfermode (patchset #6 id:100001 of https://codereview.chromium.org/1607253002/ )

Reason for revert:
Overdraw Xfer mode using new fangled glsl features

Original issue's description:
> Add gpu implementation of OverdrawXfermode
> GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1607253002
>
> Committed: https://skia.googlesource.com/skia/+/8bc3cf88bbf5e5d5724356f076931bb70a6117ba

TBR=egdaniel@google.com
# Not skipping CQ checks because original CL landed more than 1 days ago.

Review URL: https://codereview.chromium.org/1626443002

1 files changed, 11 insertions, 2 deletions

diff --git a/src/gpu/effects/GrCustomXfermode.cpp b/src/gpu/effects/GrCustomXfermode.cpp
index dccec0c599..93f20738b4 100644
--- a/src/gpu/effects/GrCustomXfermode.cpp
+++ b/src/gpu/effects/GrCustomXfermode.cpp
@@ -175,8 +175,17 @@ private:
         GrGLSLBlend::AppendMode(fragBuilder, srcColor, dstColor, outColor, xp.mode());
 
         // Apply coverage.
-        INHERITED::DefaultCoverageModulation(fragBuilder, srcCoverage, dstColor, outColor,
-                                             outColorSecondary, xp);
+        if (xp.dstReadUsesMixedSamples()) {
+            if (srcCoverage) {
+                fragBuilder->codeAppendf("%s *= %s;", outColor, srcCoverage);
+                fragBuilder->codeAppendf("%s = %s;", outColorSecondary, srcCoverage);
+            } else {
+                fragBuilder->codeAppendf("%s = vec4(1.0);", outColorSecondary);
+            }
+        } else if (srcCoverage) {
+            fragBuilder->codeAppendf("%s = %s * %s + (vec4(1.0) - %s) * %s;",
+                                     outColor, srcCoverage, outColor, srcCoverage, dstColor);
+        }
     }
 
     void onSetData(const GrGLSLProgramDataManager&, const GrXferProcessor&) override {}