Simplify adding attributes to GrGeometryProcessor
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2248323003

Review-Url: https://codereview.chromium.org/2248323003
diff --git a/src/gpu/GrPrimitiveProcessor.h b/src/gpu/GrPrimitiveProcessor.h
index d27a6f3..5239a86 100644
--- a/src/gpu/GrPrimitiveProcessor.h
+++ b/src/gpu/GrPrimitiveProcessor.h
@@ -156,8 +156,7 @@
             : fName(nullptr)
             , fType(kFloat_GrVertexAttribType)
             , fOffset(0) {}
-        Attribute(const char* name, GrVertexAttribType type,
-                  GrSLPrecision precision = kDefault_GrSLPrecision)
+        Attribute(const char* name, GrVertexAttribType type, GrSLPrecision precision)
             : fName(name)
             , fType(type)
             , fOffset(SkAlign4(GrVertexAttribTypeSize(type)))