Update from https://crrev.com/303153

cc/surfaces/surface_sequence.h

Index: cc/surfaces/surface_sequence.h
diff --git a/cc/surfaces/surface_sequence.h b/cc/surfaces/surface_sequence.h
index 4c99e458587d65065c68f206a2d0e2d156a71410..72f4bc9926fa5bf468ceab70b6513de466ea2ddd 100644
--- a/cc/surfaces/surface_sequence.h
+++ b/cc/surfaces/surface_sequence.h
@@ -5,6 +5,8 @@
 #ifndef CC_SURFACES_SURFACE_SEQUENCE_H_
 #define CC_SURFACES_SURFACE_SEQUENCE_H_
 
+#include "base/containers/hash_tables.h"
+
 namespace cc {
 
 // A per-surface-namespace sequence number that's used to coordinate
@@ -14,6 +16,7 @@ struct SurfaceSequence {
   SurfaceSequence() : id_namespace(0u), sequence(0u) {}
   SurfaceSequence(uint32_t id_namespace, uint32_t sequence)
       : id_namespace(id_namespace), sequence(sequence) {}
+  bool is_null() const { return id_namespace == 0u && sequence == 0u; }
 
   uint32_t id_namespace;
   uint32_t sequence;
@@ -35,4 +38,13 @@ inline bool operator<(const SurfaceSequence& a, const SurfaceSequence& b) {
 
 }  // namespace cc
 
+namespace BASE_HASH_NAMESPACE {
+template <>
+struct hash<cc::SurfaceSequence> {
+  size_t operator()(cc::SurfaceSequence key) const {
+    return base::HashPair(key.id_namespace, key.sequence);
+  }
+};
+}  // namespace BASE_HASH_NAMESPACE
+
 #endif  // CC_SURFACES_SURFACE_SEQUENCE_H_