VM: Move representation selection code out of the flow graph optimizer.

runtime/vm/flow_graph_compiler_arm64.cc

Index: runtime/vm/flow_graph_compiler_arm64.cc
diff --git a/runtime/vm/flow_graph_compiler_arm64.cc b/runtime/vm/flow_graph_compiler_arm64.cc
index 2a237d9cf6e5737eb4f3bc8c460aa3934d15c10e..30e421127e61d90037a650d916b5f343cfc52885 100644
--- a/runtime/vm/flow_graph_compiler_arm64.cc
+++ b/runtime/vm/flow_graph_compiler_arm64.cc
@@ -70,6 +70,13 @@ bool FlowGraphCompiler::SupportsSinCos() {
 }
 
 
+bool FlowGraphCompiler::CanConvertUnboxedMintToDouble() {
+  // ARM does not have a short instruction sequence for converting int64 to
+  // double.
+  return false;
+}
+
+
 bool FlowGraphCompiler::SupportsHardwareDivision() {
   return true;
 }