Move some isolate state setup from C++ code to JumpToExceptionHandler stub

runtime/vm/stub_code_arm64.cc

Index: runtime/vm/stub_code_arm64.cc
diff --git a/runtime/vm/stub_code_arm64.cc b/runtime/vm/stub_code_arm64.cc
index a4e43e9e59628c1ff615c12390430b2db5a7e9bc..6ccef25825dad54a0f44813fbff5894a5d0e9599 100644
--- a/runtime/vm/stub_code_arm64.cc
+++ b/runtime/vm/stub_code_arm64.cc
@@ -1819,6 +1819,7 @@ void StubCode::GenerateGetStackPointerStub(Assembler* assembler) {
 // R2: frame_pointer.
 // R3: error object.
 // R4: address of stacktrace object.
+// R5: isolate.
 // Does not return.
 void StubCode::GenerateJumpToExceptionHandlerStub(Assembler* assembler) {
   ASSERT(kExceptionObjectReg == R0);
@@ -1828,6 +1829,11 @@ void StubCode::GenerateJumpToExceptionHandlerStub(Assembler* assembler) {
   __ mov(FP, R2);  // Frame_pointer.
   __ mov(R0, R3);  // Exception object.
   __ mov(R1, R4);  // StackTrace object.
+  // Set the tag.
+  __ LoadImmediate(R2, VMTag::kScriptTagId, kNoPP);
+  __ StoreToOffset(R2, R5, Isolate::vm_tag_offset(), kNoPP);
+  // Clear top exit frame.
+  __ StoreToOffset(ZR, R5, Isolate::top_exit_frame_info_offset(), kNoPP);
   __ ret();  // Jump to the exception handler code.
 }