Introducing gpu::CommandBufferId as a distinct, IdType<...>-based type.

cc/layers/texture_layer_unittest.cc

Index: cc/layers/texture_layer_unittest.cc
diff --git a/cc/layers/texture_layer_unittest.cc b/cc/layers/texture_layer_unittest.cc
index 0cfedc35e7d406ca9d2c2fb2a5bfd15eebcdb0c5..45e59769cf00356671e9b83edeaf884d9d6f4031 100644
--- a/cc/layers/texture_layer_unittest.cc
+++ b/cc/layers/texture_layer_unittest.cc
@@ -58,7 +58,8 @@ gpu::Mailbox MailboxFromChar(char value) {
 }
 
 gpu::SyncToken SyncTokenFromUInt(uint32_t value) {
-  return gpu::SyncToken(gpu::CommandBufferNamespace::GPU_IO, 0, 0x123, value);
+  return gpu::SyncToken(gpu::CommandBufferNamespace::GPU_IO, 0,
+                        gpu::CommandBufferId::FromUnsafeValue(0x123), value);
 }
 
 class MockLayerTreeHost : public LayerTreeHost {
@@ -145,8 +146,14 @@ struct CommonMailboxObjects {
   explicit CommonMailboxObjects(SharedBitmapManager* manager)
       : mailbox_name1_(MailboxFromChar('1')),
         mailbox_name2_(MailboxFromChar('2')),
-        sync_token1_(gpu::CommandBufferNamespace::GPU_IO, 123, 0x234, 1),
-        sync_token2_(gpu::CommandBufferNamespace::GPU_IO, 123, 0x234, 2) {
+        sync_token1_(gpu::CommandBufferNamespace::GPU_IO,
+                     123,
+                     gpu::CommandBufferId::FromUnsafeValue(0x234),
+                     1),
+        sync_token2_(gpu::CommandBufferNamespace::GPU_IO,
+                     123,
+                     gpu::CommandBufferId::FromUnsafeValue(0x234),
+                     2) {
     release_mailbox1_ = base::Bind(&MockMailboxCallback::Release,
                                    base::Unretained(&mock_callback_),
                                    mailbox_name1_);