Do not call IsActiveTree() in LayerTreeImpl destructor

IsActiveTree() indirectly calls active_tree_.get() in LayerTreeHostImpl.
Since std::unique_ptr::reset() nulls out its ptr before deleting the
owned object, IsActiveTree() will always be false, and the swap promises
will always be broken with ACTIVATION_FAILS. This causes
LayerTreeHostTestSwapPromiseDuringCommit to fail when the wait for main
frame or commit condition is removed from LayerTreeTest::EndTest().

R=danakj
BUG=703263

Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I3819f76ab8f576c80faccf8db3ecd7ddb9b5954d
Reviewed-on: https://chromium-review.googlesource.com/1145920Reviewed-by: danakj <danakj@chromium.org>
Commit-Queue: Sunny Sachanandani <sunnyps@chromium.org>
Cr-Commit-Position: refs/heads/master@{#577696}

cc/trees/layer_tree_impl.cc

@@ -104,9 +104,6 @@ LayerTreeImpl::LayerTreeImpl(
 }
 
 LayerTreeImpl::~LayerTreeImpl() {
-  BreakSwapPromises(IsActiveTree() ? SwapPromise::SWAP_FAILS
-                                   : SwapPromise::ACTIVATION_FAILS);
-
   // Need to explicitly clear the tree prior to destroying this so that
   // the LayerTreeImpl pointer is still valid in the LayerImpl dtor.
   DCHECK(LayerListIsEmpty());
@@ -115,6 +112,8 @@ LayerTreeImpl::~LayerTreeImpl() {
 
 void LayerTreeImpl::Shutdown() {
   DetachLayers();
+  BreakSwapPromises(IsActiveTree() ? SwapPromise::SWAP_FAILS
+                                   : SwapPromise::ACTIVATION_FAILS);
   DCHECK(LayerListIsEmpty());
 }