ozone: Don't log on error when atomic commit fails.

DrmDevice::CommitProperties can be used to determine if a set of
properties can be commited.

In this case, CommitProperties can return false to reject those
properties.

When this happens, we shouldn't be logging on error, since the
method returning false is the intended behavior.

Bug: 
Change-Id: I89ded23cff7c54053d2d0c2ab91ef35bf348a025
Reviewed-on: https://chromium-review.googlesource.com/590710
Commit-Queue: Daniele Castagna <dcastagna@chromium.org>
Reviewed-by: Daniel Nicoara <dnicoara@chromium.org>
Cr-Commit-Position: refs/heads/master@{#490425}

ui/ozone/platform/drm/gpu/hardware_display_plane_manager_atomic.cc

@@ -74,8 +74,12 @@ bool HardwareDisplayPlaneManagerAtomic::Commit(
   if (!drm_->CommitProperties(plane_list->atomic_property_set.get(), flags,
                               crtcs.size(),
                               base::Bind(&AtomicPageFlipCallback, crtcs))) {
-    PLOG(ERROR) << "Failed to commit properties. test_only:" << std::boolalpha
-                << test_only << " error";
+    if (!test_only) {
+      PLOG(ERROR) << "Failed to commit properties for page flip.";
+    } else {
+      VPLOG(2) << "Failed to commit properties for MODE_ATOMIC_TEST_ONLY.";
+    }
+
     ResetCurrentPlaneList(plane_list);
     return false;
   }