Revert "Add external backing store JS test"

This reverts commit 5107ec2a.

Reason for revert: Test is very flaky: https://ci.chromium.org/p/v8/builders/luci.v8.ci/V8%20Linux64

Original change's description:
> Add external backing store JS test
> 
> Allow mocking the limits for ArrayBuffer allocation to simulate operating
> system OOM.
> 
> Bug: chromium:845409
> Change-Id: I38bf56a3677e1db547c774223c81e913f56cb631
> Reviewed-on: https://chromium-review.googlesource.com/1203895
> Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
> Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#55616}

TBR=ulan@chromium.org,mlippautz@chromium.org

Change-Id: I633988dba1b0a87b652e72e0e667e90122e00f6d
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: chromium:845409
Reviewed-on: https://chromium-review.googlesource.com/1206290Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55630}

src/d8.cc

@@ -135,7 +135,6 @@ class ShellArrayBufferAllocator : public ArrayBufferAllocatorBase {
 
 // ArrayBuffer allocator that never allocates over 10MB.
 class MockArrayBufferAllocator : public ArrayBufferAllocatorBase {
- protected:
   void* Allocate(size_t length) override {
     return ArrayBufferAllocatorBase::Allocate(Adjust(length));
   }
@@ -155,39 +154,6 @@ class MockArrayBufferAllocator : public ArrayBufferAllocatorBase {
   }
 };
 
-// ArrayBuffer allocator that can be equipped with a limit to simulate system
-// OOM.
-class MockArrayBufferAllocatiorWithLimit : public MockArrayBufferAllocator {
- public:
-  explicit MockArrayBufferAllocatiorWithLimit(size_t allocation_limit)
-      : space_left_(allocation_limit) {}
-
- protected:
-  void* Allocate(size_t length) override {
-    if (length > space_left_) {
-      return nullptr;
-    }
-    space_left_ -= length;
-    return MockArrayBufferAllocator::Allocate(length);
-  }
-
-  void* AllocateUninitialized(size_t length) override {
-    if (length > space_left_) {
-      return nullptr;
-    }
-    space_left_ -= length;
-    return MockArrayBufferAllocator::AllocateUninitialized(length);
-  }
-
-  void Free(void* data, size_t length) override {
-    space_left_ += length;
-    return MockArrayBufferAllocator::Free(data, length);
-  }
-
- private:
-  std::atomic<size_t> space_left_;
-};
-
 // Predictable v8::Platform implementation. Worker threads are disabled, idle
 // tasks are disallowed, and the time reported by {MonotonicallyIncreasingTime}
 // is deterministic.
@@ -2938,8 +2904,6 @@ bool Shell::SetOptions(int argc, char* argv[]) {
 
   v8::V8::SetFlagsFromCommandLine(&argc, argv, true);
   options.mock_arraybuffer_allocator = i::FLAG_mock_arraybuffer_allocator;
-  options.mock_arraybuffer_allocator_limit =
-      i::FLAG_mock_arraybuffer_allocator_limit;
 
   // Set up isolated source groups.
   options.isolate_sources = new SourceGroup[options.num_isolates];
@@ -3398,18 +3362,8 @@ int Shell::Main(int argc, char* argv[]) {
   Isolate::CreateParams create_params;
   ShellArrayBufferAllocator shell_array_buffer_allocator;
   MockArrayBufferAllocator mock_arraybuffer_allocator;
-  const size_t memory_limit =
-      options.mock_arraybuffer_allocator_limit * options.num_isolates;
-  MockArrayBufferAllocatiorWithLimit mock_arraybuffer_allocator_with_limit(
-      memory_limit >= options.mock_arraybuffer_allocator_limit
-          ? memory_limit
-          : std::numeric_limits<size_t>::max());
   if (options.mock_arraybuffer_allocator) {
-    if (memory_limit) {
-      Shell::array_buffer_allocator = &mock_arraybuffer_allocator_with_limit;
-    } else {
     Shell::array_buffer_allocator = &mock_arraybuffer_allocator;
-    }
   } else {
     Shell::array_buffer_allocator = &shell_array_buffer_allocator;
   }

src/d8.h

@@ -369,7 +369,6 @@ class ShellOptions {
   bool test_shell;
   bool expected_to_throw;
   bool mock_arraybuffer_allocator;
-  size_t mock_arraybuffer_allocator_limit = 0;
   bool enable_inspector;
   int num_isolates;
   v8::ScriptCompiler::CompileOptions compile_options;

src/flag-definitions.h

@@ -1152,9 +1152,6 @@ DEFINE_ARGS(js_arguments,
             "Pass all remaining arguments to the script. Alias for \"--\".")
 DEFINE_BOOL(mock_arraybuffer_allocator, false,
             "Use a mock ArrayBuffer allocator for testing.")
-DEFINE_SIZE_T(mock_arraybuffer_allocator_limit, 0,
-              "Memory limit for mock ArrayBuffer allocator used to simulate "
-              "OOM for testing.")
 
 //
 // GDB JIT integration flags.

test/mjsunit/external-backing-store-gc.js

-// Copyright 2018 the V8 project authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-// Flags: --mock-arraybuffer-allocator --mock-arraybuffer-allocator-limit=800000000
-
-for (var i = 0; i < 1024; i++) {
-  let garbage = new ArrayBuffer(1024*1024);
-}