Align base::hash_map with C++11.

cc/trees/layer_tree_impl.h

Index: cc/trees/layer_tree_impl.h
diff --git a/cc/trees/layer_tree_impl.h b/cc/trees/layer_tree_impl.h
index e1b2335a8f9d81504a3c34e6585b5358a44e8b90..b18a33128dfbec91101cd1c712d37c75f5c6336e 100644
--- a/cc/trees/layer_tree_impl.h
+++ b/cc/trees/layer_tree_impl.h
@@ -18,17 +18,6 @@
 #include "cc/output/renderer.h"
 #include "cc/resources/ui_resource_client.h"
 
-#if defined(COMPILER_GCC)
-namespace BASE_HASH_NAMESPACE {
-template<>
-struct hash<cc::LayerImpl*> {
-  size_t operator()(cc::LayerImpl* ptr) const {
-    return hash<size_t>()(reinterpret_cast<size_t>(ptr));
-  }
-};
-}  // namespace BASE_HASH_NAMESPACE
-#endif  // COMPILER
-
 namespace base {
 namespace debug {
 class TracedValue;