gpu: Add sync token dependencies to flush metadata.

This CL adds a list of sync tokens, for which waits were inserted in the
command buffer, to the flush message. This information will be used by
the gpu scheduler to deschedule a command buffer until all sync tokens
of its next flush are released.

Also includes some minor cleanup.

R=jbauman@chromium.org
BUG=514813
CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel

Review-Url: https://codereview.chromium.org/2727573003
Cr-Commit-Position: refs/heads/master@{#456961}

diff --git a/cc/raster/gpu_raster_buffer_provider.cc b/cc/raster/gpu_raster_buffer_provider.cc
index 2e253dc..208068a 100644
--- a/cc/raster/gpu_raster_buffer_provider.cc
+++ b/cc/raster/gpu_raster_buffer_provider.cc

@@ -200,8 +200,8 @@
   if (!sync_token.HasData())
     return true;
 
-  // IsSyncTokenSignalled is threadsafe, no need for worker context lock.
-  return worker_context_provider_->ContextSupport()->IsSyncTokenSignalled(
+  // IsSyncTokenSignaled is thread-safe, no need for worker context lock.
+  return worker_context_provider_->ContextSupport()->IsSyncTokenSignaled(
       sync_token);
 }