Add javascript compatibility warnings for integer values and integral double

runtime/lib/identical.cc

Index: runtime/lib/identical.cc
===================================================================
--- runtime/lib/identical.cc	(revision 37016)
+++ runtime/lib/identical.cc	(working copy)
@@ -38,8 +38,30 @@
   GET_NATIVE_ARGUMENT(Instance, b, arguments->NativeArgAt(1));
   const bool is_identical = a.IsIdenticalTo(b);
   if (FLAG_warn_on_javascript_compatibility) {
-    if (!is_identical && a.IsString() && String::Cast(a).Equals(b)) {
-      JSWarning("strings that are equal are also identical");
+    if (!is_identical) {
+      if (a.IsString()) {
+        if (String::Cast(a).Equals(b)) {
+          JSWarning("strings that are equal are also identical");
+        }
+      } else if (a.IsInteger()) {
+        if (b.IsDouble()) {
+          const int64_t a_value = Integer::Cast(a).AsInt64Value();
+          const double b_value = Double::Cast(b).value();
+          if (a_value == floor(b_value)) {
+            JSWarning("integer value and integral double value that are equal "
+                      "are also identical");
+          }
+        }
+      } else if (a.IsDouble()) {
+        if (b.IsInteger()) {
+          const double a_value = Double::Cast(a).value();
+          const int64_t b_value = Integer::Cast(b).AsInt64Value();
+          if (floor(a_value) == b_value) {
+            JSWarning("integral double value and integer value that are equal "
+                      "are also identical");
+          }
+        }
+      }
     }
   }
   return Bool::Get(is_identical).raw();