Optimize testing for an index's existence in packed Arrays

This patch introduces a new inline runtime function,
%_HasFastPackedElements(), and uses it both in the implementation
of the 'in' operator and in the array builtins to speed
up testing for the existence of an index in an array.

In testing with the microbenchmark on the attached bug,
for example, the runtime goes from 326ms to 66ms.

A reviewer might ask whether the HAS_INDEX macro is worthwhile,
and I tried the same example without it, which pushed the
microbenchmark up to 157ms. So it seems it's worth it to
avoid the function call to IN() if we know we're dealing
with arrays and numbers.

BUG=v8:3701
LOG=n

Review URL: https://codereview.chromium.org/754863002

Cr-Commit-Position: refs/heads/master@{#25665}
Cleanup: Remove NativesCollection<.>::*Raw* methods.

These methods for used for compressed libraries, where GetSource* functions
contained the compressed sources and [GS]etRawSource* the uncompressed
sources. This is dead code since the API no longer supports compression.

(If you need/want compressed sources, use the external startup data and
 compress/uncompress on the Embedder's side.)

BUG=

Review URL: https://codereview.chromium.org/772853003

Cr-Commit-Position: refs/heads/master@{#25666}
Make template scan related function take a template<bool> parameter

This is for performance. Having to do the test in every Advance was too
expensive.

BUG=438991, v8:3230
LOG=N
R=dslomov@chromium.org, marja

Review URL: https://codereview.chromium.org/766193003

Cr-Commit-Position: refs/heads/master@{#25667}
Optimize add/set/delete operations for string keys in Maps and Sets

Review URL: https://codereview.chromium.org/773993002

Cr-Commit-Position: refs/heads/master@{#25668}
Add js-perf-test for ES6 class default constructor

BUG=v8:3330
LOG=N
TBR=dslomov@chromium.org

Review URL: https://codereview.chromium.org/754523004

Cr-Commit-Position: refs/heads/master@{#25669}
Revert of Optimize add/set/delete operations for string keys in Maps and Sets (patchset #5 id:70001 of https://codereview.chromium.org/773993002/)

Reason for revert:
Caused test failures in mjsunit/es6/collections with --deopt-every-n-times=1

Original issue's description:
> Optimize add/set/delete operations for string keys in Maps and Sets

TBR=dslomov@chromium.org,arv@chromium.org
NOTREECHECKS=true
NOTRY=true

Review URL: https://codereview.chromium.org/777233003

Cr-Commit-Position: refs/heads/master@{#25670}
MIPS: Fixed environment handling for LFlooringDivI.

Port c16b8f6cbbe295abf3fab2f6b9f4a4632db4cf6b

TEST=mjsunit/regress/regress-437765
BUG=

Review URL: https://codereview.chromium.org/750213003

Cr-Commit-Position: refs/heads/master@{#25671}