Revert of Avoid number range holes in bitset types. (patchset #5 id:80001 of https://codereview.chromium.org/759013003/)

Reason for revert:
For breaking the waterfall (run-json-stringify test).

Original issue's description:
> Avoid number range holes in bitset types.
>
> BUG=

TBR=rossberg@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=

Review URL: https://codereview.chromium.org/794663002

Cr-Commit-Position: refs/heads/master@{#25756}
Ensure class prototype objects have the right Map::constructor field

The null constructor they had previously could be observed as crashes in
the V8 API's Object::CreationContext() method and in Object.observe.

BUG=v8:3750
LOG=n
R=arv@chromium.org, dslomov@chromium.org

Review URL: https://codereview.chromium.org/787763005

Cr-Commit-Position: refs/heads/master@{#25757}
Create optimized inline versions of Map and Set initialization

Review URL: https://codereview.chromium.org/779173010

Cr-Commit-Position: refs/heads/master@{#25758}
Optimize Object.seal and Object.preventExtensions

They both now run fast (due to utilizing transitions instead of always
creating new maps) and sealed or non-extensible objects can stay in
fast mode after transitioning.

This almost entirely reuses the code for transitioning objects
frozen by Object.freeze(), with the added benefit of freeing
up a bit on the map (we no longer keep track of frozen-ness,
as that bit wasn't used for anything interesting).

BUG=v8:3662,chromium:115960
LOG=y

Review URL: https://codereview.chromium.org/776143005

Cr-Commit-Position: refs/heads/master@{#25759}
Update strict mode function declaration tests before block scoping.

R=arv@chromium.org,marja@chromium.org
BUG=v8:2198
LOG=N

Review URL: https://codereview.chromium.org/788143004

Cr-Commit-Position: refs/heads/master@{#25760}
Ship ES6 block scoping.

R=rossberg@chromium.org
BUG=v8:2198
LOG=Y

Review URL: https://codereview.chromium.org/792543002

Cr-Commit-Position: refs/heads/master@{#25761}
Implement the `RegExp.prototype.flags` getter

TEST=mjsunit/harmony
BUG=v8:3751
LOG=N

Review URL: https://codereview.chromium.org/770333005

Cr-Commit-Position: refs/heads/master@{#25762}
Create optimized versions of the Map/Set clear method

This completes the first round of optimizations for Map and Set.
All non-key-dependent methods now have a Hydrogen version, and
for keyed methods, string versions are optimized.

Review URL: https://codereview.chromium.org/796503002

Cr-Commit-Position: refs/heads/master@{#25763}
Fix crash in V8 during serializing objects requiring alignment.

Review URL: https://codereview.chromium.org/793753002

Cr-Commit-Position: refs/heads/master@{#25764}
[turbofan] Fix typing of typed array loads/stores.

R=svenpanne@chromium.org

Review URL: https://codereview.chromium.org/794113002

Cr-Commit-Position: refs/heads/master@{#25765}
Switch icu repo to icu.git in v8 DEPS.

This ports https://codereview.chromium.org/769413004 to v8
DEPS.

BUG=chromium:438401
LOG=n
TBR=jshin@chromium.org

Review URL: https://codereview.chromium.org/796813002

Cr-Commit-Position: refs/heads/master@{#25766}
[V8] Report v8::AfterCompile and v8::CompileError to listener on pause

V8 didn't report compile events on pause before this patch. These events can be important for listener. For example, DevTools allows user to execute some JS code on pause and needs to show correct stack trace in message from it.

BUG=396013
R=yurys@chromium.org

Review URL: https://codereview.chromium.org/781623004

Cr-Commit-Position: refs/heads/master@{#25767}
Implement Math.log2 via ported extract from fdlibm.

Adapted from Raymond Toy's (rtoy@chromium.org) port, extracted from fdlibm's pow implementation.

R=rtoy@chromium.org
BUG=v8:3579
LOG=N

Review URL: https://codereview.chromium.org/786823003

Cr-Commit-Position: refs/heads/master@{#25768}
Disable invalid DCHECK_EQ in serializer.cc

BUG=none
R=mvstanton@chromium.org,yangguo@chromium.org
LOG=n

Review URL: https://codereview.chromium.org/791363002

Cr-Commit-Position: refs/heads/master@{#25769}
remove Isolate::debugger_initialized_

It's never used.

BUG=none
R=dcarney@chromium.org
LOG=n

Review URL: https://codereview.chromium.org/797543002

Cr-Commit-Position: refs/heads/master@{#25770}
[turbofan]: Port lea changes to ia32

Review URL: https://codereview.chromium.org/747283005

Cr-Commit-Position: refs/heads/master@{#25771}
[turbofan] commit allocated registers early

R=bmeurer@chromium.org
BUG=441107
LOG=N

Review URL: https://codereview.chromium.org/795043003

Cr-Commit-Position: refs/heads/master@{#25772}
[turbofan] Mark arm64 cbz/cbnz tbz/tbnz instructions as branch instructions.

The instruction selector now selects pseudo instructions: CompareAndBranch or
TestAndBranch which are associated with their continuations so that generic
code in the code generator will treat them as branch instruction and will be
able to apply optimization like avoiding branches when the code can falltrhough.

R=bmeurer@chromium.org

Review URL: https://codereview.chromium.org/798553002

Cr-Commit-Position: refs/heads/master@{#25773}
Disable generating of code cache if the debugger is loaded

BUG=440880
R=yangguo@chromium.org,dcarney@chromium.org,vogelheim@chromium.org
LOG=n

Review URL: https://codereview.chromium.org/796823002

Cr-Commit-Position: refs/heads/master@{#25774}
[turbofan] Avoid some redundant checks of unordered comparison on arm/arm64.

R=bmeurer@chromium.org

Review URL: https://codereview.chromium.org/793303002

Cr-Commit-Position: refs/heads/master@{#25775}