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

runtime/vm/snapshot.h

Index: runtime/vm/snapshot.h
diff --git a/runtime/vm/snapshot.h b/runtime/vm/snapshot.h
index 1d8f585320b9aeaa431f494ad4678e5bdda10f2c..96911666f784201808fb510313d865599f1d1dfe 100644
--- a/runtime/vm/snapshot.h
+++ b/runtime/vm/snapshot.h
@@ -51,6 +51,7 @@ class RawExceptionHandlers;
 class RawField;
 class RawFloat32x4;
 class RawFloat64x2;
+class RawFraction;
 class RawFunction;
 class RawGrowableObjectArray;
 class RawICData;
@@ -449,6 +450,7 @@ class SnapshotReader : public BaseReader {
   RawInstance* NewInstance();
   RawMint* NewMint(int64_t value);
   RawBigint* NewBigint();
+  RawFraction* NewFraction();
   RawTypedData* NewTypedData(intptr_t class_id, intptr_t len);
   RawDouble* NewDouble(double value);
   RawUnresolvedClass* NewUnresolvedClass();
@@ -613,6 +615,7 @@ class SnapshotReader : public BaseReader {
   friend class ContextScope;
   friend class ExceptionHandlers;
   friend class Field;
+  friend class Fraction;
   friend class Function;
   friend class GrowableObjectArray;
   friend class ICData;