emitChild() takes an outputColor instead of generating one

src/gpu/gl/GrGLFragmentProcessor.h

Index: src/gpu/gl/GrGLFragmentProcessor.h
diff --git a/src/gpu/gl/GrGLFragmentProcessor.h b/src/gpu/gl/GrGLFragmentProcessor.h
index b8e2afc1bb61c387e16b62a9a76990bac82f47b0..e11d28b26ba2b1f8440742f84fd5ce6b16fcf49a 100644
--- a/src/gpu/gl/GrGLFragmentProcessor.h
+++ b/src/gpu/gl/GrGLFragmentProcessor.h
@@ -80,7 +80,12 @@ public:
         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