Validate DrawArcOp inputs

Skip nans because they cause Skia asserts.

Bug: 752757
Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I8ac1ac10c785dad5eb74dd33107f1febb7e361c4
Reviewed-on: https://chromium-review.googlesource.com/627394
Commit-Queue: enne <enne@chromium.org>
Reviewed-by: Vladimir Levin <vmpstr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#496503}

cc/paint/paint_op_buffer.h

@@ -361,7 +361,10 @@ class CC_PAINT_EXPORT DrawArcOp final : public PaintOpWithFlags {
                               const PaintFlags* flags,
                               SkCanvas* canvas,
                               const PlaybackParams& params);
-  bool IsValid() const { return flags.IsValid() && oval.isFinite(); }
+  bool IsValid() const {
+    return flags.IsValid() && oval.isFinite() && std::isfinite(start_angle) &&
+           std::isfinite(sweep_angle);
+  }
   HAS_SERIALIZATION_FUNCTIONS();
 
   SkRect oval;