ARM: make sure that the expected code size is computed in predictable scope.

src/assembler.h

Index: src/assembler.h
diff --git a/src/assembler.h b/src/assembler.h
index 1b4c76540757a17de02e341327d7f4dacc812064..ee7026a8753466d7096686bbf664ee727368a696 100644
--- a/src/assembler.h
+++ b/src/assembler.h
@@ -158,8 +158,10 @@ class DontEmitDebugCodeScope BASE_EMBEDDED {
 // snapshot and the running VM.
 class PredictableCodeSizeScope {
  public:
+  explicit PredictableCodeSizeScope(AssemblerBase* assembler);
   PredictableCodeSizeScope(AssemblerBase* assembler, int expected_size);
   ~PredictableCodeSizeScope();
+  void ExpectSize(int expected_size) { expected_size_ = expected_size; }
 
  private:
   AssemblerBase* assembler_;