Implement tidyeval for benchplot()(#2816)

Closes #2699

Author: dpseidel

NEWS.md

@@ -1,5 +1,7 @@
 # ggplot2 3.0.0.9000
 
+*   `benchplot()` now uses tidy evaluation (@dpseidel, #2699).
+    
 *   `fortify()` now displays a more informative error message for
     `grouped_df()` objects when dplyr is not installed (@jimhester, #2822).
 

R/bench.r

@@ -7,9 +7,14 @@
 #' @examples
 #' benchplot(ggplot(mtcars, aes(mpg, wt)) + geom_point())
 #' benchplot(ggplot(mtcars, aes(mpg, wt)) + geom_point() + facet_grid(. ~ cyl))
-benchplot <- function(x) {
+#'
+#' # With tidy eval:
+#' p <- expr(ggplot(mtcars, aes(mpg, wt)) + geom_point())
+#' benchplot(!!p)
 
-  construct <- system.time(force(x))
+benchplot <- function(x) {
+  x <- enquo(x)
+  construct <- system.time(x <- rlang::eval_tidy(x))
   stopifnot(inherits(x, "ggplot"))
 
   build <- system.time(data <- ggplot_build(x))