cc: Clean up max frames/swaps pending usage.

cc/scheduler/scheduler.cc

Index: cc/scheduler/scheduler.cc
diff --git a/cc/scheduler/scheduler.cc b/cc/scheduler/scheduler.cc
index 072086fe0dd262ea9bc03e66ccc4d2cb91c08d5b..a17c656bbe87d3f724cdcd38d6e2ca150027c3e6 100644
--- a/cc/scheduler/scheduler.cc
+++ b/cc/scheduler/scheduler.cc
@@ -194,6 +194,9 @@ void Scheduler::SetNeedsPrepareTiles() {
 }
 
 void Scheduler::SetMaxSwapsPending(int max) {
+  // TODO(brianderson): Remove all callers of this function.
+  DCHECK_EQ(1, max) << "Surface and CompositorTimingHistory do not support "
+                       "multiple pending swaps.";
   state_machine_.SetMaxSwapsPending(max);
 }