Reland of Move tracing namespace from base::debug to base::trace_event.

cc/quads/shared_quad_state.h

Index: cc/quads/shared_quad_state.h
diff --git a/cc/quads/shared_quad_state.h b/cc/quads/shared_quad_state.h
index ebf7d11986e01a30661fd73ac7a15bddbb312058..0db23e195200b309c7752c87f9d456e7a4612b2e 100644
--- a/cc/quads/shared_quad_state.h
+++ b/cc/quads/shared_quad_state.h
@@ -12,11 +12,17 @@
 #include "ui/gfx/transform.h"
 
 namespace base {
-namespace debug {
+namespace trace_event {
 class TracedValue;
 }
 class Value;
+
+// TODO(ssid): remove these aliases after the tracing clients are moved to the
+// new trace_event namespace. See crbug.com/451032. ETA: March 2015
+namespace debug {
+using ::base::trace_event::TracedValue;
 }
+}  // namespace base
 
 namespace cc {