Create GLSLUniformHandler class for gpu backend

BUG=skia:

Review URL: https://codereview.chromium.org/1490283004
diff --git a/src/gpu/effects/GrPorterDuffXferProcessor.cpp b/src/gpu/effects/GrPorterDuffXferProcessor.cpp
index 42a9631..69e77cf 100644
--- a/src/gpu/effects/GrPorterDuffXferProcessor.cpp
+++ b/src/gpu/effects/GrPorterDuffXferProcessor.cpp
@@ -16,8 +16,8 @@
 #include "GrXferProcessor.h"
 #include "glsl/GrGLSLBlend.h"
 #include "glsl/GrGLSLFragmentShaderBuilder.h"
-#include "glsl/GrGLSLProgramBuilder.h"
 #include "glsl/GrGLSLProgramDataManager.h"
+#include "glsl/GrGLSLUniformHandler.h"
 #include "glsl/GrGLSLXferProcessor.h"
 
 /**
@@ -545,8 +545,8 @@
     }
 
 private:
-    void emitBlendCodeForDstRead(GrGLSLXPBuilder* pb,
-                                 GrGLSLXPFragmentBuilder* fragBuilder,
+    void emitBlendCodeForDstRead(GrGLSLXPFragmentBuilder* fragBuilder,
+                                 GrGLSLUniformHandler* uniformHandler,
                                  const char* srcColor,
                                  const char* srcCoverage,
                                  const char* dstColor,