Distance field fixes for Android

src/gpu/GrOvalRenderer.cpp

Index: src/gpu/GrOvalRenderer.cpp
diff --git a/src/gpu/GrOvalRenderer.cpp b/src/gpu/GrOvalRenderer.cpp
index ac33a5cc5d9e7665283f5c5bd27f51ee54088d5e..23ce230bfa8ffa6008b29774d283b323cc2c0632 100644
--- a/src/gpu/GrOvalRenderer.cpp
+++ b/src/gpu/GrOvalRenderer.cpp
@@ -232,8 +232,9 @@ public:
             builder->fsCodeAppend("\tfloat grad_dot = dot(grad, grad);\n");
             // we need to clamp the length^2 of the gradiant vector to a non-zero value, because
             // on the Nexus 4 the undefined result of inversesqrt(0) drops out an entire tile
-            // TODO: restrict this to Adreno-only
-            builder->fsCodeAppend("\tgrad_dot = max(grad_dot, 1.0e-4);\n");
+            if (builder->ctxInfo().caps()->dropsTileOnZeroDivide()) {
+                builder->fsCodeAppend("\tgrad_dot = max(grad_dot, 1.0e-4);\n");
+            }
             builder->fsCodeAppend("\tfloat invlen = inversesqrt(grad_dot);\n");
             builder->fsCodeAppend("\tfloat edgeAlpha = clamp(0.5-test*invlen, 0.0, 1.0);\n");
 
@@ -380,8 +381,9 @@ public:
             builder->fsCodeAppend("\tfloat grad_dot = dot(grad, grad);\n");
             // we need to clamp the length^2 of the gradiant vector to a non-zero value, because
             // on the Nexus 4 the undefined result of inversesqrt(0) drops out an entire tile
-            // TODO: restrict this to Adreno-only
-            builder->fsCodeAppend("\tgrad_dot = max(grad_dot, 1.0e-4);\n");
+            if (builder->ctxInfo().caps()->dropsTileOnZeroDivide()) {
+                builder->fsCodeAppend("\tgrad_dot = max(grad_dot, 1.0e-4);\n");
+            }
             builder->fsCodeAppend("\tfloat invlen = inversesqrt(grad_dot);\n");
             if (kHairline == ellipseEffect.getMode()) {
                 // can probably do this with one step