Replace the use CharacterStreams in Heap::AllocateSymbolInternal and String::ComputeHash

src/heap.h

Index: src/heap.h
diff --git a/src/heap.h b/src/heap.h
index 068c44e713f5569515606e2b582caee994ea17f1..6bf4e87a230d5a9d676bde059126609dfc4ae94d 100644
--- a/src/heap.h
+++ b/src/heap.h
@@ -764,12 +764,16 @@ class Heap {
         Vector<const uc16> str,
         uint32_t hash_field);
 
-  MUST_USE_RESULT MaybeObject* AllocateInternalSymbol(
-      unibrow::CharacterStream* buffer, int chars, uint32_t hash_field);
+  template<typename T>
+  static inline bool IsOneByte(T t, int chars);
 
-  MUST_USE_RESULT MaybeObject* AllocateExternalSymbol(
-      Vector<const char> str,
-      int chars);
+  template<typename T>
+  MUST_USE_RESULT inline MaybeObject* AllocateInternalSymbol(
+      T t, int chars, uint32_t hash_field);
+
+  template<bool is_one_byte, typename T>
+  MUST_USE_RESULT MaybeObject* AllocateInternalSymbol(
+      T t, int chars, uint32_t hash_field);
 
   // Allocates and partially initializes a String.  There are two String
   // encodings: ASCII and two byte.  These functions allocate a string of the