Add faster, but unsafe version of LoadInternalField.

src/fast-accessor-assembler.h

Index: src/fast-accessor-assembler.h
diff --git a/src/fast-accessor-assembler.h b/src/fast-accessor-assembler.h
index 41337a2b09d8883efd2243e785040da4db4bfde3..452684ff5680aeeecbecfb944b274e65416be531 100644
--- a/src/fast-accessor-assembler.h
+++ b/src/fast-accessor-assembler.h
@@ -54,6 +54,15 @@ class FastAccessorAssembler {
   ValueId IntegerConstant(int int_constant);
   ValueId GetReceiver();
   ValueId LoadInternalField(ValueId value_id, int field_no);
+
+  // Unsafe but fast version, does NOT perform any sanity checks.

[vogelheim, 2016/07/27 09:50:56]

nitpick: Your description is correct, but unnecessarily dramatic. :) How about
this:

Loads internal field and assumes the object is indeed a valid API object with
the proper internal fields present.

The intended use is to call this on an object whose structure has already been
checked previously, e.g. the accessor's receiver, which is map-checked before
the fast accessor is called on it. Using this on an arbitrary object will result
in unsafe memory accesses.

[Alfonso, 2016/07/28 14:39:13]

Acknowledged. I lost objectivity.

+  // This is plain unsafe, basically gives read access to memory.
+  // Use ONLY if can be verified 100% that all access paths have proper
+  // checks; and the checks are indeed redundant. Security have clear priority
+  // over performance, there's no trade-off to play here. Use the safe method
+  // otherwise, it's quite fast.
+  ValueId LoadInternalFieldUnsafe(ValueId value_id, int field_no);
+
   ValueId LoadValue(ValueId value_id, int offset);
   ValueId LoadObject(ValueId value_id, int offset);