emitChild() takes an outputColor instead of generating one

src/gpu/gl/GrGLFragmentProcessor.h

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrGLFragmentProcessor_DEFINED
 #define GrGLFragmentProcessor_DEFINED
 
@@ skipping 62 matching lines @@
     void setData(const GrGLProgramDataManager& pdman, const GrFragmentProcessor& processor);
 
     static void GenKey(const GrProcessor&, const GrGLSLCaps&, GrProcessorKeyBuilder*) {}
 
     int numChildProcessors() const { return fChildProcessors.count(); }
 
     GrGLFragmentProcessor* childProcessor(int index) const {
         return fChildProcessors[index];
     }
 
-    void emitChild(int childIndex, const char* inputColor, SkString* outputColor, EmitArgs& args);
+    /** Will emit the code of a child proc in its own scope. Pass in the parent's EmitArgs and
+     * emitChild will automatically extract the coords and samplers of that child and pass them
+     * on to the child's emitCode().  Also, any uniforms or functions emitted by the child will
+     * have their names mangled to prevent redefinitions.
+     */
+    void emitChild(int childIndex, const char* inputColor, const char* outputColor, EmitArgs& args);
 
 protected:
     /** A GrGLFragmentProcessor instance can be reused with any GrFragmentProcessor that produces
     the same stage key; this function reads data from a GrFragmentProcessor and uploads any
     uniform variables required by the shaders created in emitCode(). The GrFragmentProcessor
     parameter is guaranteed to be of the same type that created this GrGLFragmentProcessor and
     to have an identical processor key as the one that created this GrGLFragmentProcessor.  */
     // TODO update this to pass in GrFragmentProcessor
     virtual void onSetData(const GrGLProgramDataManager&, const GrProcessor&) {}
 
 private:
     SkTArray<GrGLFragmentProcessor*, true> fChildProcessors;
 
     friend class GrFragmentProcessor;
     typedef GrGLProcessor INHERITED;
 };
 
 #endif