cc: The recent texture manager bug uncovered some unnecessary code

cc/prioritized_texture.cc

Index: cc/prioritized_texture.cc
diff --git a/cc/prioritized_texture.cc b/cc/prioritized_texture.cc
index 37ad64fedf8c11781c3fc2e36390e75c017168ca..9fc25710cff9186ad85c36226ec8fc9941995ae5 100644
--- a/cc/prioritized_texture.cc
+++ b/cc/prioritized_texture.cc
@@ -189,4 +189,11 @@ void CCPrioritizedTexture::Backing::updateInDrawingImplTree()
         ASSERT(m_priorityAtLastPriorityUpdate == CCPriorityCalculator::lowestPriority());
 }
 
+void CCPrioritizedTexture::returnBackingTexture()
+{
+    ASSERT(m_manager || !m_backing);
+    if (m_manager)
+        m_manager->returnBackingTexture(this);
+}
+
 } // namespace cc