buffet: fix signed warnings

Newer gcc complains about signed mismatch like so:
error: comparison between signed and unsigned integer expressions [

BUG=chromium:423463
TEST=None

Change-Id: I8ab4a4c834f5972c66ed7cbfc54e9648bcfb201f
Reviewed-on: https://chromium-review.googlesource.com/230011
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>

buffet/commands/dbus_command_dispatcher_unittest.cc

diff --git a/buffet/commands/dbus_command_dispatcher_unittest.cc b/buffet/commands/dbus_command_dispatcher_unittest.cc
index f11dd56..af15c1d 100644
--- a/buffet/commands/dbus_command_dispatcher_unittest.cc
+++ b/buffet/commands/dbus_command_dispatcher_unittest.cc
@@ -109,7 +109,7 @@
   }
 
   DBusCommandProxy* FindProxy(CommandInstance* command_instance) {
-    CHECK_EQ(command_instance->proxies_.size(), 1);
+    CHECK_EQ(command_instance->proxies_.size(), 1U);
     return static_cast<DBusCommandProxy*>(command_instance->proxies_[0].get());
   }
 

buffet/commands/dbus_command_proxy_unittest.cc

diff --git a/buffet/commands/dbus_command_proxy_unittest.cc b/buffet/commands/dbus_command_proxy_unittest.cc
index 94b4906..3cb907d 100644
--- a/buffet/commands/dbus_command_proxy_unittest.cc
+++ b/buffet/commands/dbus_command_proxy_unittest.cc
@@ -107,7 +107,7 @@
   }
 
   DBusCommandProxy* GetCommandProxy() const {
-    CHECK_EQ(command_instance_->proxies_.size(), 1);
+    CHECK_EQ(command_instance_->proxies_.size(), 1U);
     return static_cast<DBusCommandProxy*>(command_instance_->proxies_[0].get());
   }
 

buffet/states/state_change_queue.cc

diff --git a/buffet/states/state_change_queue.cc b/buffet/states/state_change_queue.cc
index f7775ba..f27b339 100644
--- a/buffet/states/state_change_queue.cc
+++ b/buffet/states/state_change_queue.cc
@@ -10,7 +10,7 @@
 
 StateChangeQueue::StateChangeQueue(size_t max_queue_size)
     : max_queue_size_(max_queue_size) {
-  CHECK_GT(max_queue_size_, 0) << "Max queue size must not be zero";
+  CHECK_GT(max_queue_size_, 0U) << "Max queue size must not be zero";
 }
 
 bool StateChangeQueue::NotifyPropertiesUpdated(