Specialize breakpoint stubs by set of live registers of the stubs they are intercepting.

runtime/vm/runtime_entry_arm.cc

Index: runtime/vm/runtime_entry_arm.cc
diff --git a/runtime/vm/runtime_entry_arm.cc b/runtime/vm/runtime_entry_arm.cc
index 1dbd0196e620034571f34c0069321abbd06b7566..2ab3ba8e8bf4fe4aff9c286292cdd1ea516450e6 100644
--- a/runtime/vm/runtime_entry_arm.cc
+++ b/runtime/vm/runtime_entry_arm.cc
@@ -20,7 +20,7 @@ namespace dart {
 // function. Input for the stub is as follows:
 //   SP : points to the arguments and return value array.
 //   R5 : address of the runtime function to call.
-//   R4 : number of arguments to the call as Smi.
+//   R4 : number of arguments to the call.
 void RuntimeEntry::Call(Assembler* assembler, intptr_t argument_count) const {
   // Compute the effective address. When running under the simulator,
   // this is a redirection address that forces the simulator to call
@@ -47,8 +47,9 @@ void RuntimeEntry::Call(Assembler* assembler, intptr_t argument_count) const {
   } else {
     // Argument count is not checked here, but in the runtime entry for a more
     // informative error message.
+    ASSERT((entry & kSmiTagMask) == 0);
     __ LoadImmediate(R5, entry);
-    __ LoadImmediate(R4, Smi::RawValue(argument_count));
+    __ LoadImmediate(R4, argument_count);
     __ BranchLink(&StubCode::CallToRuntimeLabel());
   }
 }