[surfaces] use DEFAULT_MAX_FRAMES_PENDING if OutputSurface doesn't specify it.

To match LTHI, change the max frames pending calculation to output DEFAULT_MAX_FRAMES_PENDING if the output surface reports 0.

Review URL: https://codereview.chromium.org/885933002

Cr-Commit-Position: refs/heads/master@{#313800}

cc/surfaces/display.cc

@@ -198,9 +198,11 @@ SurfaceId Display::CurrentSurfaceId() {
 }
 
 int Display::GetMaxFramesPending() {
-  if (!output_surface_)
-    return OutputSurface::DEFAULT_MAX_FRAMES_PENDING;
-  return output_surface_->capabilities().max_frames_pending;
+  int max_frames_pending =
+      output_surface_ ? output_surface_->capabilities().max_frames_pending : 0;
+  if (max_frames_pending <= 0)
+    max_frames_pending = OutputSurface::DEFAULT_MAX_FRAMES_PENDING;
+  return max_frames_pending;
 }
 
 }  // namespace cc