Add synthetic delay testing framework

cc/trees/thread_proxy.cc

Index: cc/trees/thread_proxy.cc
diff --git a/cc/trees/thread_proxy.cc b/cc/trees/thread_proxy.cc
index 4f2f488eae8e5805ee2caff3dbda557bcc8709da..90602c42882cbb30e67077ad5c3ba74707c2eb65 100644
--- a/cc/trees/thread_proxy.cc
+++ b/cc/trees/thread_proxy.cc
@@ -8,6 +8,7 @@
 
 #include "base/auto_reset.h"
 #include "base/bind.h"
+#include "base/debug/synthetic_delay.h"
 #include "base/debug/trace_event.h"
 #include "base/metrics/histogram.h"
 #include "cc/debug/benchmark_instrumentation.h"
@@ -1026,6 +1027,7 @@ DrawSwapReadbackResult ThreadProxy::DrawSwapReadbackInternal(
     bool forced_draw,
     bool swap_requested,
     bool readback_requested) {
+  SYNTHETIC_DELAY("cc.draw_and_swap");
   DrawSwapReadbackResult result;
   result.did_draw = false;
   result.did_swap = false;