Test that GrFragmentProcessors work without input colors.

src/gpu/effects/GrConstColorProcessor.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "effects/GrConstColorProcessor.h"
 #include "gl/GrGLFragmentProcessor.h"
 #include "gl/builders/GrGLProgramBuilder.h"
 
 class GLConstColorProcessor : public GrGLFragmentProcessor {
 public:
     GLConstColorProcessor() : fPrevColor(GrColor_ILLEGAL) {}
 
     void emitCode(EmitArgs& args) override {
         GrGLFragmentBuilder* fsBuilder = args.fBuilder->getFragmentShaderBuilder();
         const char* colorUni;
         fColorUniform = args.fBuilder->addUniform(GrGLProgramBuilder::kFragment_Visibility,
                                             kVec4f_GrSLType, kMedium_GrSLPrecision, "constantColor",
                                             &colorUni);
-        switch (args.fFp.cast<GrConstColorProcessor>().inputMode()) {
+        GrConstColorProcessor::InputMode mode = args.fFp.cast<GrConstColorProcessor>().inputMode();
+        if (!args.fInputColor) {
+            mode = GrConstColorProcessor::kIgnore_InputMode;
+        }
+        switch (mode) {
             case GrConstColorProcessor::kIgnore_InputMode:
                 fsBuilder->codeAppendf("%s = %s;", args.fOutputColor, colorUni);
                 break;
             case GrConstColorProcessor::kModulateRGBA_InputMode:
                 fsBuilder->codeAppendf("%s = %s * %s;", args.fOutputColor, args.fInputColor,
                                        colorUni);
                 break;
             case GrConstColorProcessor::kModulateA_InputMode:
                 fsBuilder->codeAppendf("%s = %s.a * %s;", args.fOutputColor, args.fInputColor,
                                        colorUni);
@@ skipping 86 matching lines @@
             color = 0;
             break;
         case 2:
             color = d->fRandom->nextULessThan(0x100);
             color = color | (color << 8) | (color << 16) | (color << 24);
             break;
     }
     InputMode mode = static_cast<InputMode>(d->fRandom->nextULessThan(kInputModeCnt));
     return GrConstColorProcessor::Create(color, mode);
 }