Generation of dot files through visitor.Added type info to .dot.

visitor.h: Fixed formatting.
type_inference.cc: Changed GetSSAConsumers() to return pointer.
sea_node.h, sea.cc: Removed ToDot classes functions.
instruction_nodes.h: Added acessor for SSA producers.
                     Marked GetUses() as const.
sea.h: Marked fields as const.
frontend.cc: Changed .dot generation code.
code_gen.h: Fixed include to have full path.

Change-Id: Ia84371c171c4537d9cf2f56644baa075f1706df1