Refactoring codegen for delete.

Refactoring codegen for delete.
 * keep handling of VariableProxy and Property together
 * place clauses in the order of discovery

The refactoring is inspired by the strict mode delete changes.
While placing the ASSERT(strict_mode_flag() == kNonStrictMode)
for the variable case, I realized that better order of the if clauses
would make the code more readable, and also make it eas to place my assert.

BUG=
TEST=

[Martin Maly, 2011-02-14 06:03:21]

While working on the strict mode delete I found that I can reorder the if
clauses for delete codegen and hopefully make the code slightly more readable,
and I could also place assert I am introducing for the strict mode delete work
in more general place:

var != NULL ==> cannot be in strict mode ==> ASSERT(strict_mode_flag() ==
kNonStrictMode)

Thank you!
Martin

[Kevin Millikin (Chromium), 2011-02-14 06:45:58]

LGTM.