allocator: rename use_experimental_allocator_shim to use_allocator_shim

base/allocator/README.md

 This document describes how malloc / new calls are routed in the various Chrome
 platforms.
 
 Bare in mind that the chromium codebase does not always just use `malloc()`.
 Some examples:
  - Large parts of the renderer (Blink) use two home-brewed allocators,
    PartitionAlloc and BlinkGC (Oilpan).
  - Some subsystems, such as the V8 JavaScript engine, handle memory management
    autonomously.
  - Various parts of the codebase use abstractions such as `SharedMemory` or
@@ skipping 69 matching lines @@
 `../../third_party/tcmalloc` (currently, the actual location is defined in the
 allocator.gyp file). The third party sources use a vendor-branch SCM pattern to
 track Chromium-specific changes independently from upstream changes.
 
 The general intent is to push local changes upstream so that over
 time we no longer need any forked files.
 
 
 Unified allocator shim
 ----------------------
-On most platform, Chrome overrides the malloc / operator new symbols (and
+On most platforms, Chrome overrides the malloc / operator new symbols (and
 corresponding free / delete and other variants). This is to enforce security
 checks and lately to enable the
 [memory-infra heap profiler][url-memory-infra-heap-profiler].  
 Historically each platform had its special logic for defining the allocator
 symbols in different places of the codebase. The unified allocator shim is
 a project aimed to unify the symbol definition and allocator routing logic in
 a central place.
 
  - Full documentation: [Allocator shim design doc][url-allocator-shim].
- - Current state: Available and enabled by default on Linux, CrOS and Android.
+ - Current state: Available and enabled by default on Android, CrOS, Linux,
+   Mac OS and Windows.
  - Tracking bug: [https://crbug.com/550886][crbug.com/550886].
- - Build-time flag: `use_experimental_allocator_shim`.
+ - Build-time flag: `use_allocator_shim`.
 
 **Overview of the unified allocator shim**  
 The allocator shim consists of three stages:
 ```
 +-------------------------+    +-----------------------+    +----------------+
 |     malloc & friends    | -> |       shim layer      | -> |   Routing to   |
 |    symbols definition   |    |     implementation    |    |    allocator   |
 +-------------------------+    +-----------------------+    +----------------+
 | - libc symbols (malloc, |    | - Security checks     |    | - tcmalloc     |
 |   calloc, free, ...)    |    | - Chain of dispatchers|    | - glibc        |
@@ skipping 74 matching lines @@
 Related links
 -------------
 - [Unified allocator shim doc - Feb 2016][url-allocator-shim]
 - [Allocator cleanup doc - Jan 2016][url-allocator-cleanup]
 - [Proposal to use PartitionAlloc as default allocator](https://crbug.com/339604)
 - [Memory-Infra: Tools to profile memory usage in Chrome](/docs/memory-infra/README.md)
 
 [url-allocator-cleanup]: https://docs.google.com/document/d/1V77Kgp_4tfaaWPEZVxNevoD02wXiatnAv7Ssgr0hmjg/edit?usp=sharing
 [url-memory-infra-heap-profiler]: /docs/memory-infra/heap_profiler.md
 [url-allocator-shim]: https://docs.google.com/document/d/1yKlO1AO4XjpDad9rjcBOI15EKdAGsuGO_IeZy0g0kxo/edit?usp=sharing