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

runtime/vm/stub_code_ia32.cc

Index: runtime/vm/stub_code_ia32.cc
diff --git a/runtime/vm/stub_code_ia32.cc b/runtime/vm/stub_code_ia32.cc
index 33f280392c867923b367e76b3ebb5731da777a25..88fb684abcbc9aa5704ec171d539f9a7238ab236 100644
--- a/runtime/vm/stub_code_ia32.cc
+++ b/runtime/vm/stub_code_ia32.cc
@@ -1786,15 +1786,22 @@ void StubCode::GenerateGetStackPointerStub(Assembler* assembler) {
 // TOS + 3: frame_pointer
 // TOS + 4: exception object
 // TOS + 5: stacktrace object
+// TOS + 6: isolate
 // No Result.
 void StubCode::GenerateJumpToExceptionHandlerStub(Assembler* assembler) {
   ASSERT(kExceptionObjectReg == EAX);
   ASSERT(kStackTraceObjectReg == EDX);
+  __ movl(CTX, Address(ESP, 6 * kWordSize));  // Load target isolate.
   __ movl(kStackTraceObjectReg, Address(ESP, 5 * kWordSize));
   __ movl(kExceptionObjectReg, Address(ESP, 4 * kWordSize));
   __ movl(EBP, Address(ESP, 3 * kWordSize));  // Load target frame_pointer.
   __ movl(EBX, Address(ESP, 1 * kWordSize));  // Load target PC into EBX.
   __ movl(ESP, Address(ESP, 2 * kWordSize));  // Load target stack_pointer.
+  // Set tag.
+  __ movl(Address(CTX, Isolate::vm_tag_offset()),
+          Immediate(VMTag::kScriptTagId));
+  // Clear top exit frame.
+  __ movl(Address(CTX, Isolate::top_exit_frame_info_offset()), Immediate(0));
   __ jmp(EBX);  // Jump to the exception handler code.
 }