Fix clobbered register when setting this_function variable.

src/arm/full-codegen-arm.cc

Index: src/arm/full-codegen-arm.cc
diff --git a/src/arm/full-codegen-arm.cc b/src/arm/full-codegen-arm.cc
index a2f24400a4fc53612d0b5123f618266a89f75bfb..32e7a545378906854db9cd68f5b67b1073f7e5b1 100644
--- a/src/arm/full-codegen-arm.cc
+++ b/src/arm/full-codegen-arm.cc
@@ -243,6 +243,10 @@ void FullCodeGenerator::Generate() {
   Variable* this_function_var = scope()->this_function_var();
   if (this_function_var != nullptr) {
     Comment cmnt(masm_, "[ This function");
+    if (!function_in_register) {
+      __ ldr(r1, MemOperand(fp, JavaScriptFrameConstants::kFunctionOffset));
+      function_in_register = true;
+    }
     SetVar(this_function_var, r1, r0, r2);
   }