Remove MutexLock from the argument.  Use AssertHeld instead.

Change-Id: I43beab4cf30cbb6b2d3c383d492240d4a1ac8068
diff --git a/src/compiler_llvm/compiler_llvm.h b/src/compiler_llvm/compiler_llvm.h
index 07ffa61..7481c8c 100644
--- a/src/compiler_llvm/compiler_llvm.h
+++ b/src/compiler_llvm/compiler_llvm.h
@@ -83,9 +83,9 @@
   CompiledInvokeStub* CreateInvokeStub(bool is_static, char const *shorty);
 
  private:
-  void EnsureCompilationUnit(MutexLock& GUARD);
+  void EnsureCompilationUnit();
 
-  void Materialize(MutexLock& GUARD);
+  void Materialize();
 
   bool IsBitcodeFileNameAvailable() const {
     return !bitcode_filename_.empty();