Use the code point iterator in equality comparisons to C strings.

runtime/vm/object.h

Index: runtime/vm/object.h
diff --git a/runtime/vm/object.h b/runtime/vm/object.h
index d2914dcf2c17103b4a7174d71655eddb148dcfe0..cee8d823bc4c8dea06c803c11a78721b43d13c32 100644
--- a/runtime/vm/object.h
+++ b/runtime/vm/object.h
@@ -3761,9 +3761,17 @@ class String : public Instance {
   inline bool Equals(const String& str,
                      intptr_t begin_index,  // begin index on 'str'.
                      intptr_t len) const;  // len on 'str'.
-  bool Equals(const char* str) const;
+
+  // Compares to a '\0' terminated array of UTF-8 encoded characters.
+  bool Equals(const char* cstr) const;
+
+  // Compares to an array of UTF-8 encoded characters.
   bool Equals(const uint8_t* characters, intptr_t len) const;
+
+  // Compares to an array of UTF-16 encoded characters.
   bool Equals(const uint16_t* characters, intptr_t len) const;
+
+  // Compares to an array of UTF-32 encoded characters.
   bool Equals(const uint32_t* characters, intptr_t len) const;
 
   virtual bool Equals(const Instance& other) const;