[arm] Eliminate OperandConverter Float32 and Float64 register methods.

src/compiler/instruction.h

Index: src/compiler/instruction.h
diff --git a/src/compiler/instruction.h b/src/compiler/instruction.h
index 6e9480bf7b92fc319141d2cc1c453ba67d688c4a..af7e592e5f93c4a0596c3c6d7b280c3160faca15 100644
--- a/src/compiler/instruction.h
+++ b/src/compiler/instruction.h
@@ -439,8 +439,9 @@ class LocationOperand : public InstructionOperand {
   }
 
   DoubleRegister GetDoubleRegister() const {
-    // TODO(bbudge) Tighten this test to IsDoubleRegister when all code
-    // generators are changed to use the correct Get*Register method.
+    // On platforms where FloatRegister, DoubleRegister, and Simd128Register
+    // are all the same type, it's convenient to treat everything as a
+    // DoubleRegister, so be lax about type checking here.
     DCHECK(IsFPRegister());
     return DoubleRegister::from_code(register_code());
   }