Add missing cmath import in material-color-utilities

See: https://github.com/material-foundation/material-color-utilities/blob/main/cpp/palettes/tones.cc

--- a/third_party/material_color_utilities/src/cpp/palettes/tones.cc
+++ b/third_party/material_color_utilities/src/cpp/palettes/tones.cc
@@ -19,6 +19,8 @@
 #include "cpp/cam/cam.h"
 #include "cpp/cam/hct.h"
 
+#include <cmath>
+
 namespace material_color_utilities {
 
 TonalPalette::TonalPalette(Argb argb) : key_color_(0.0, 0.0, 0.0) {
@@ -67,7 +69,7 @@ Hct TonalPalette::createKeyColor(double hue, double chroma) {
     // case where requested chroma is 16.51, and the closest chroma is 16.49.
     // Error is minimized, but when rounded and displayed, requested chroma
     // is 17, key color's chroma is 16.
-    if (round(chroma) == round(smallest_delta_hct.get_chroma())) {
+    if (std::round(chroma) == std::round(smallest_delta_hct.get_chroma())) {
       return smallest_delta_hct;
     }
     Hct hct_add(hue, chroma, start_tone + delta);