Fix GrConvexPolyEffect to deal with line paths.

src/gpu/effects/GrConvexPolyEffect.cpp

Index: src/gpu/effects/GrConvexPolyEffect.cpp
diff --git a/src/gpu/effects/GrConvexPolyEffect.cpp b/src/gpu/effects/GrConvexPolyEffect.cpp
index cf874cfa52604e1666ddecad3fec720d1063279a..7b78305bb1e014d8a8d5ca2597ff00c942ac884a 100644
--- a/src/gpu/effects/GrConvexPolyEffect.cpp
+++ b/src/gpu/effects/GrConvexPolyEffect.cpp
@@ -8,6 +8,7 @@
 #include "GrConvexPolyEffect.h"
 #include "GrInvariantOutput.h"
 #include "SkPathPriv.h"
+#include "effects/GrConstColorProcessor.h"
 #include "glsl/GrGLSLFragmentProcessor.h"
 #include "glsl/GrGLSLFragmentShaderBuilder.h"
 #include "glsl/GrGLSLProgramDataManager.h"
@@ -254,7 +255,16 @@ GrFragmentProcessor* GrConvexPolyEffect::Create(GrPrimitiveEdgeType type, const
     SkScalar edges[3 * kMaxEdges];
 
     SkPathPriv::FirstDirection dir;
-    SkAssertResult(SkPathPriv::CheapComputeFirstDirection(path, &dir));
+    // The only way this should fail is if the clip is effectively a infinitely thin line. In that
+    // case nothing is inside the clip. It'd be nice to detect this at a higher level and either
+    // skip the draw or omit the clip element.
+    if (!SkPathPriv::CheapComputeFirstDirection(path, &dir)) {
+        if (GrProcessorEdgeTypeIsInverseFill(type)) {
+            return GrConstColorProcessor::Create(0xFFFFFFFF,
+                                                 GrConstColorProcessor::kModulateRGBA_InputMode);
+        }
+        return GrConstColorProcessor::Create(0, GrConstColorProcessor::kIgnore_InputMode);
+    }
 
     SkVector t;
     if (nullptr == offset) {