Use a lock to deal with concurrent access to the m_evictedBackings

cc/tiled_layer_unittest.cc

Index: cc/tiled_layer_unittest.cc
diff --git a/cc/tiled_layer_unittest.cc b/cc/tiled_layer_unittest.cc
index 52c4bea447e087bca607e7ac8eef88675b919d74..b1336c82e567341786aa67aa668be0ad8750ddd6 100644
--- a/cc/tiled_layer_unittest.cc
+++ b/cc/tiled_layer_unittest.cc
@@ -94,9 +94,12 @@ public:
     };
     void resourceManagerClearAllMemory(PrioritizedResourceManager* resourceManager, ResourceProvider* resourceProvider)
     {
-        DebugScopedSetImplThreadAndMainThreadBlocked implThreadAndMainThreadBlocked(m_proxy);
-        resourceManager->clearAllMemory(resourceProvider);
-        resourceManager->reduceMemory(resourceProvider);
+        {
+            DebugScopedSetImplThreadAndMainThreadBlocked implThreadAndMainThreadBlocked(m_proxy);
+            resourceManager->clearAllMemory(resourceProvider);
+            resourceManager->reduceMemory(resourceProvider);
+        }
+        resourceManager->unlinkAndClearEvictedBackings();
     }
     void updateTextures()
     {