[compiler] Verify that type feedback vector structure is the same on recompile.

src/compiler.cc

Index: src/compiler.cc
diff --git a/src/compiler.cc b/src/compiler.cc
index 1815c9a8d6441176ba61503aa3ba2186ddc30abe..574048682238c0a8c56316c7ba0f6c03ad8729f4 100644
--- a/src/compiler.cc
+++ b/src/compiler.cc
@@ -211,11 +211,14 @@ bool CompilationInfo::ShouldSelfOptimize() {
 
 
 void CompilationInfo::EnsureFeedbackVector() {
-  if (feedback_vector_.is_null() ||
-      feedback_vector_->SpecDiffersFrom(function()->feedback_vector_spec())) {
+  if (feedback_vector_.is_null()) {
     feedback_vector_ = isolate()->factory()->NewTypeFeedbackVector(
         function()->feedback_vector_spec());
   }
+
+  // It's very important that recompiles do not alter the structure of the
+  // type feedback vector.
+  CHECK(!feedback_vector_->SpecDiffersFrom(function()->feedback_vector_spec()));
 }