Fraction class prototype and test (not to be committed).

runtime/vm/intermediate_language.cc

Index: runtime/vm/intermediate_language.cc
diff --git a/runtime/vm/intermediate_language.cc b/runtime/vm/intermediate_language.cc
index a2a9d2768a3eeca3dde6f90e183d07cca37b1d3b..faa7c143b204a54bf7897f9bea6be48048da39c7 100644
--- a/runtime/vm/intermediate_language.cc
+++ b/runtime/vm/intermediate_language.cc
@@ -2404,7 +2404,8 @@ static bool MayBeBoxableNumber(intptr_t cid) {
   return (cid == kDynamicCid) ||
          (cid == kMintCid) ||
          (cid == kBigintCid) ||
-         (cid == kDoubleCid);
+         (cid == kDoubleCid) ||
+         (cid == kFractionCid);
 }
 
 
@@ -2423,8 +2424,8 @@ static bool MaybeNumber(CompileType* type) {
 static Definition* CanonicalizeStrictCompare(StrictCompareInstr* compare,
                                              bool* negated) {
   // Use propagated cid and type information to eliminate number checks.
-  // If one of the inputs is not a boxable number (Mint, Double, Bigint), or
-  // is not a subtype of num, no need for number checks.
+  // If one of the inputs is not a boxable number (Mint, Double, Bigint,
+  // Fraction), or  is not a subtype of num, no need for number checks.
   if (compare->needs_number_check()) {
     if (!MayBeBoxableNumber(compare->left()->Type()->ToCid()) ||
         !MayBeBoxableNumber(compare->right()->Type()->ToCid()))  {