Fixed crashes exposed though fuzzing.

src/x64/macro-assembler-x64.h

Index: src/x64/macro-assembler-x64.h
diff --git a/src/x64/macro-assembler-x64.h b/src/x64/macro-assembler-x64.h
index 4bea4612d5fdb030b5ea198bbdff50997d90edca..f7bf1ca7446dc1750e77c601b6b125fdd97dca81 100644
--- a/src/x64/macro-assembler-x64.h
+++ b/src/x64/macro-assembler-x64.h
@@ -792,6 +792,11 @@ class MacroAssembler: public Assembler {
       Label* on_fail,
       Label::Distance near_jump = Label::kFar);
 
+  void EmitSeqStringSetCharCheck(Register string,
+                                 Register index,
+                                 Register value,
+                                 uint32_t encoding_mask);
+
   // Checks if the given register or operand is a unique name
   void JumpIfNotUniqueName(Register reg, Label* not_unique_name,
                            Label::Distance distance = Label::kFar);
@@ -1058,6 +1063,12 @@ class MacroAssembler: public Assembler {
   // Propagate an uncatchable exception out of the current JS stack.
   void ThrowUncatchable(Register value);
 
+  // Throw a message string as an exception.
+  void Throw(BailoutReason reason);
+
+  // Throw a message string as an exception if a condition is not true.
+  void ThrowIf(Condition cc, BailoutReason reason);
+
   // ---------------------------------------------------------------------------
   // Inline caching support