Save/restore only live registers in the generator suspend/resume.

src/isolate.cc

Index: src/isolate.cc
diff --git a/src/isolate.cc b/src/isolate.cc
index 6094e30d2fa8100eaf7af09f17576f761b111594..74a85b2d9a2b8a612e16227b96df58444abe524d 100644
--- a/src/isolate.cc
+++ b/src/isolate.cc
@@ -1318,6 +1318,7 @@ Object* Isolate::UnwindAndFindHandler() {
         // position of the exception handler. The special builtin below will
         // take care of continuing to dispatch at that position. Also restore
         // the correct context for the handler from the interpreter register.
+        CHECK(js_frame->ReadInterpreterRegister(context_reg)->IsContext());
         Context* context =
             Context::cast(js_frame->ReadInterpreterRegister(context_reg));
         js_frame->PatchBytecodeOffset(static_cast<int>(offset));