Add proper includes for usage of the CityHash functions.

gpu/command_buffer/service/gles2_cmd_decoder.cc

Index: gpu/command_buffer/service/gles2_cmd_decoder.cc
diff --git a/gpu/command_buffer/service/gles2_cmd_decoder.cc b/gpu/command_buffer/service/gles2_cmd_decoder.cc
index 3553a7addd858e7cb242b33d42bf54ab83c16e32..a6306dfa9b076eb34c1484dc664ca7cbbdbefd75 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder.cc
+++ b/gpu/command_buffer/service/gles2_cmd_decoder.cc
@@ -57,6 +57,7 @@
 #include "gpu/command_buffer/service/texture_manager.h"
 #include "gpu/command_buffer/service/vertex_array_manager.h"
 #include "gpu/command_buffer/service/vertex_attrib_manager.h"
+#include "third_party/smhasher/src/City.h"
 #include "ui/gl/gl_bindings.h"
 #include "ui/gl/gl_fence.h"
 #include "ui/gl/gl_image.h"
@@ -71,9 +72,6 @@
 #include "base/win/win_util.h"
 #endif
 
-// TODO(zmo): we can't include "City.h" due to type def conflicts.
-extern uint64 CityHash64(const char*, size_t);
-
 namespace gpu {
 namespace gles2 {