Improvements and clustering for the .dot file generation.

Dot clusters are used to show SEA IR regions.
Passing around dex_file for improved instruction  text representation.
SeaGraph now stores the dex file.
Removed all .dot edges except ssa edges and inter-region control flow.
Changed color to gray for ssa edges and kept black for control flow.
Consistently labeled SSA edges with virtual register number.
Replaced stringstream with StringPrintf.

Change-Id: I67d9d92e594d3f2de94eec1c78a64f3972ae60b1
diff --git a/compiler/sea_ir/frontend.cc b/compiler/sea_ir/frontend.cc
index 8fc1cf8..ebc767c 100644
--- a/compiler/sea_ir/frontend.cc
+++ b/compiler/sea_ir/frontend.cc
@@ -40,7 +40,7 @@
   // NOTE: Instead of keeping the convention from the Dalvik frontend.cc
   //       and silencing the cpplint.py warning, I just corrected the formatting.
   VLOG(compiler) << "Compiling " << PrettyMethod(method_idx, dex_file) << "...";
-  sea_ir::SeaGraph* sg = sea_ir::SeaGraph::GetCurrentGraph();
+  sea_ir::SeaGraph* sg = sea_ir::SeaGraph::GetCurrentGraph(dex_file);
   sg->CompileMethod(code_item, class_def_idx, method_idx, dex_file);
   sg->DumpSea("/tmp/temp.dot");
   CHECK(0 && "No SEA compiled function exists yet.");