Make addUniform take a precision

Review URL: https://codereview.chromium.org/788733003
diff --git a/src/effects/SkTableColorFilter.cpp b/src/effects/SkTableColorFilter.cpp
index db25a6f..942bae7 100644
--- a/src/effects/SkTableColorFilter.cpp
+++ b/src/effects/SkTableColorFilter.cpp
@@ -343,7 +343,8 @@
                                   const TextureSamplerArray& samplers) {
     const char* yoffsets;
     fRGBAYValuesUni = builder->addUniform(GrGLFPBuilder::kFragment_Visibility,
-                                          kVec4f_GrSLType, "yoffsets", &yoffsets);
+                                          kVec4f_GrSLType, kDefault_GrSLPrecision,
+                                          "yoffsets", &yoffsets);
     static const float kColorScaleFactor = 255.0f / 256.0f;
     static const float kColorOffsetFactor = 1.0f / 512.0f;
     GrGLFPFragmentBuilder* fsBuilder = builder->getFragmentShaderBuilder();