Do div-by-zero check for all gpus in ellipse/rr effects.

src/gpu/effects/GrOvalEffect.cpp

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrOvalEffect.h"
 
 #include "gl/GrGLEffect.h"
@@ skipping 299 matching lines @@
                                          &ellipseName);
     const char* fragmentPos = builder->fragmentPosition();
 
     // d is the offset to the ellipse center
     builder->fsCodeAppendf("\t\tvec2 d = %s.xy - %s.xy;\n", fragmentPos, ellipseName);
     builder->fsCodeAppendf("\t\tvec2 Z = d * %s.zw;\n", ellipseName);
     // implicit is the evaluation of (x/rx)^2 + (y/ry)^2 - 1.
     builder->fsCodeAppend("\t\tfloat implicit = dot(Z, d) - 1.0;\n");
     // grad_dot is the squared length of the gradient of the implicit.
     builder->fsCodeAppendf("\t\tfloat grad_dot = 4.0 * dot(Z, Z);\n");
-    if (builder->ctxInfo().caps()->dropsTileOnZeroDivide()) {
-        builder->fsCodeAppend("\t\tgrad_dot = max(grad_dot, 1.0e-4);\n");
-    }
+    // avoid calling inversesqrt on zero.
+    builder->fsCodeAppend("\t\tgrad_dot = max(grad_dot, 1.0e-4);\n");
     builder->fsCodeAppendf("\t\tfloat approx_dist = implicit * inversesqrt(grad_dot);\n");
 
     switch (ee.getEdgeType()) {
         case kFillAA_GrEffectEdgeType:
             builder->fsCodeAppend("\t\tfloat alpha = clamp(0.5 - approx_dist, 0.0, 1.0);\n");
             break;
         case kInverseFillAA_GrEffectEdgeType:
             builder->fsCodeAppend("\t\tfloat alpha = clamp(0.5 + approx_dist, 0.0, 1.0);\n");
             break;
         case kFillBW_GrEffectEdgeType:
@@ skipping 39 matching lines @@
         w /= 2;
         return CircleEffect::Create(edgeType, SkPoint::Make(oval.fLeft + w, oval.fTop + w), w);
     } else {
         w /= 2;
         h /= 2;
         return EllipseEffect::Create(edgeType, SkPoint::Make(oval.fLeft + w, oval.fTop + h), w, h);
     }
 
     return NULL;
 }