cc: Fix incorrect LTHI shutdown logic

Landing this fix for enne@. Original description by enne@:

It's possible that if there has never been an activation (implying no root
layer on the active tree), then the trees will not be cleared during
LayerTreeHostImpl's destructor. Given the comment in the destructor about
animation, this seems to be problematic enough.

Issue 251722 is about a case where the tile manager tries to activate the tree
during its destruction but because the trees haven't been cleared yet, it
thinks this is a supported operation. This is fixed by always destroying the
trees in the destructor.

BUG=251722
NOTRY=true

Review URL: https://chromiumcodereview.appspot.com/16983013

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@208251 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 7 insertions, 9 deletions

diff --git a/cc/trees/layer_tree_host_impl.cc b/cc/trees/layer_tree_host_impl.cc
index 4fe0871..316aeeb 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -227,15 +227,13 @@ LayerTreeHostImpl::~LayerTreeHostImpl() {
     input_handler_client_ = NULL;
   }
 
-  if (active_tree_->root_layer()) {
-    ClearRenderSurfaces();
-    // The layer trees must be destroyed before the layer tree host. We've
-    // made a contract with our animation controllers that the registrar
-    // will outlive them, and we must make good.
-    recycle_tree_.reset();
-    pending_tree_.reset();
-    active_tree_.reset();
-  }
+  ClearRenderSurfaces();
+  // The layer trees must be destroyed before the layer tree host. We've
+  // made a contract with our animation controllers that the registrar
+  // will outlive them, and we must make good.
+  recycle_tree_.reset();
+  pending_tree_.reset();
+  active_tree_.reset();
 }
 
 void LayerTreeHostImpl::BeginCommit() {}