[zion] Add per-process CapabilityTable object

Store this information in it's own object to make the API clearer.

zion/capability/capability_table.cpp

@@ -0,0 +1,41 @@
+#include "capability/capability_table.h"
+
+CapabilityTable::CapabilityTable() {}
+
+uint64_t CapabilityTable::AddExistingCapability(const RefPtr<Capability>& cap) {
+  MutexHolder h(lock_);
+  cap->set_id(next_cap_id_++);
+  capabilities_.PushBack(cap);
+  return cap->id();
+}
+
+RefPtr<Capability> CapabilityTable::GetCapability(uint64_t id) {
+  MutexHolder h(lock_);
+  auto iter = capabilities_.begin();
+  while (iter != capabilities_.end()) {
+    if (*iter && iter->id() == id) {
+      return *iter;
+    }
+    ++iter;
+  }
+  dbgln("Bad cap access %u", id);
+  dbgln("Num caps: %u", capabilities_.size());
+  return {};
+}
+
+RefPtr<Capability> CapabilityTable::ReleaseCapability(uint64_t id) {
+  MutexHolder h(lock_);
+  auto iter = capabilities_.begin();
+  while (iter != capabilities_.end()) {
+    if (*iter && iter->id() == id) {
+      // FIXME: Do an actual release here.
+      auto cap = *iter;
+      *iter = {nullptr};
+      return cap;
+    }
+    ++iter;
+  }
+  dbgln("Bad cap release: %u", id);
+  dbgln("Num caps: %u", capabilities_.size());
+  return {};
+}