Add a simple check for V4 cross reference table

Some unknown software generates cross reference table with the
claimed object numbers are all off by one. Add a simple verification
function to detect this scenario, thus have a chance to rebuild
the correct cross reference table.

To avoid unnecessary checks and potiential performance hit, we only
check for the very first non free entry.

BUG=602650

Review URL: https://codereview.chromium.org/1910063004
diff --git a/DEPS b/DEPS
index 855dfe2..2e6f801 100644
--- a/DEPS
+++ b/DEPS
@@ -67,6 +67,13 @@
   '+third_party/base',
 ]
 
+specific_include_rules = {
+  # Allow embedder tests to use public APIs.
+  "(.*embeddertest\.cpp)": [
+      "+public",
+  ]
+}
+
 hooks = [
   # Pull GN binaries. This needs to be before running GYP below.
   {