Revert "make enum santizer fatal"

This reverts commit 166dbd3135e02d0e874591db02f9b1ad7fc961f5.

Reason for revert: illegal is not advanced, docs

Original change's description:
> make enum santizer fatal
> 
> This enum sanitizer checks that all the values of the enum we use fall
> within the range of the enumerated values.
> 
> The main thing this helps point out is that the size of enum types in
> C++ need only be large enough to hold the largest declared value; larger
> values are undefined.  In practice, most enums are implemented as ints
> for compatibility with C, so while this hasn't pointed out anything
> egregiously broken, the sanitizer has found a couple possibly dangerous
> situations in our codebase.
> 
> For most types using values outside the enum range, we can just
> explicitly size them to int.  This makes their de facto size de jure.
> 
> But we need to actually make GrBlendEquation and GrBlendCoeff not store
> values outside their enumerated range.  They're packed into bitfields
> that really can't represent those (negative) values.  So for these I've
> added new kIllegal values to the enums, forcing us to deal with our
> once-silent illegal values a bit more explicitly.
> 
> Change-Id: Ib617694cf1aaa83ae99289e9e760f49cb6393a2f
> Reviewed-on: https://skia-review.googlesource.com/c/168484
> Reviewed-by: Brian Osman <brianosman@google.com>

TBR=mtklein@chromium.org,mtklein@google.com,brianosman@google.com

Change-Id: I691c08092340a6273e442c0f098b844f7d0363ba
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://skia-review.googlesource.com/c/168581
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
diff --git a/src/gpu/effects/GrCustomXfermode.cpp b/src/gpu/effects/GrCustomXfermode.cpp
index 3d39c54..5c35260 100644
--- a/src/gpu/effects/GrCustomXfermode.cpp
+++ b/src/gpu/effects/GrCustomXfermode.cpp
@@ -46,10 +46,7 @@
     GR_STATIC_ASSERT(kHSLSaturation_GrBlendEquation == (int)SkBlendMode::kSaturation + EQ_OFFSET);
     GR_STATIC_ASSERT(kHSLColor_GrBlendEquation == (int)SkBlendMode::kColor + EQ_OFFSET);
     GR_STATIC_ASSERT(kHSLLuminosity_GrBlendEquation == (int)SkBlendMode::kLuminosity + EQ_OFFSET);
-
-    // There's an illegal GrBlendEquation that corresponds to no SkBlendMode, hence the extra +1.
-    GR_STATIC_ASSERT(kGrBlendEquationCnt == (int)SkBlendMode::kLastMode + 1 + 1 + EQ_OFFSET);
-
+    GR_STATIC_ASSERT(kGrBlendEquationCnt == (int)SkBlendMode::kLastMode + 1 + EQ_OFFSET);
     return static_cast<GrBlendEquation>((int)mode + EQ_OFFSET);
 #undef EQ_OFFSET
 }
@@ -82,7 +79,7 @@
     CustomXP(bool hasMixedSamples, SkBlendMode mode, GrProcessorAnalysisCoverage coverage)
             : INHERITED(kCustomXP_ClassID, true, hasMixedSamples, coverage)
             , fMode(mode)
-            , fHWBlendEquation(kIllegal_GrBlendEquation) {
+            , fHWBlendEquation(static_cast<GrBlendEquation>(-1)) {
     }
 
     const char* name() const override { return "Custom Xfermode"; }
@@ -90,7 +87,7 @@
     GrGLSLXferProcessor* createGLSLInstance() const override;
 
     SkBlendMode mode() const { return fMode; }
-    bool hasHWBlendEquation() const { return kIllegal_GrBlendEquation != fHWBlendEquation; }
+    bool hasHWBlendEquation() const { return -1 != static_cast<int>(fHWBlendEquation); }
 
     GrBlendEquation hwBlendEquation() const {
         SkASSERT(this->hasHWBlendEquation());