Start enabling platform_canvas_unittests on Linux

skia/BUILD.gn

Index: skia/BUILD.gn
diff --git a/skia/BUILD.gn b/skia/BUILD.gn
index e9d2872a5ebe5ad938d7eb70a11f0c9d95f37d9f..19ffd107022e410c297d8c9c87a204fc26cc20ca 100644
--- a/skia/BUILD.gn
+++ b/skia/BUILD.gn
@@ -662,7 +662,7 @@ test("skia_unittests") {
     "ext/skia_utils_mac_unittest.mm",
   ]
 
-  if (!is_win && !is_mac) {
+  if (!is_win && !is_mac && !use_cairo) {
     sources -= [ "ext/platform_canvas_unittest.cc" ]
   }
 
@@ -684,6 +684,12 @@ test("skia_unittests") {
       "//skia/public/interfaces:test_interfaces",
     ]
   }
+
+  if (is_linux) {
+    if (use_pango) {
+      configs += [ "//build/config/linux/pangocairo" ]
+    }
+  }
 }
 
 if (!is_ios) {