Cleanups: addressed your comments from https://codereview.chromium.org/14962008/

runtime/vm/dart_api_impl.cc

Index: runtime/vm/dart_api_impl.cc
===================================================================
--- runtime/vm/dart_api_impl.cc	(revision 22880)
+++ runtime/vm/dart_api_impl.cc	(working copy)
@@ -1326,7 +1326,7 @@
   if (int_obj.IsNull()) {
     RETURN_TYPE_ERROR(isolate, integer, Integer);
   }
-  ASSERT(!BigintOperations::FitsIntoMint(Bigint::Cast(int_obj)));
+  ASSERT(!BigintOperations::FitsIntoInt64(Bigint::Cast(int_obj)));
   *fits = false;
   return Api::Success(isolate);
 }
@@ -1402,8 +1402,8 @@
     return Api::Success(isolate);
   } else {
     const Bigint& bigint = Bigint::Cast(int_obj);
-    if (BigintOperations::FitsIntoMint(bigint)) {
-      *value = BigintOperations::ToMint(bigint);
+    if (BigintOperations::FitsIntoInt64(bigint)) {
+      *value = BigintOperations::ToInt64(bigint);
       return Api::Success(isolate);
     }
   }
@@ -1949,7 +1949,7 @@
       // Check for a non-canonical Mint range value.
       ASSERT(retval.IsBigint());
       const Bigint& bigint = Bigint::Handle();
-      if (BigintOperations::FitsIntoMint(bigint)) {
+      if (BigintOperations::FitsIntoInt64(bigint)) {
         int64_t bigint_value = bigint.AsInt64Value();
         if (bigint_value >= kIntptrMin && bigint_value <= kIntptrMax) {
           *len = static_cast<intptr_t>(bigint_value);