Update Windows-specific docs for the clang rewriting tool.

docs/clang_tool_refactoring.md

 # Clang Tool Refactoring
 
 [TOC]
 
 ## Introduction
 
 Clang tools can help with global refactorings of Chromium code. Clang tools can
 take advantage of clang's AST to perform refactorings that would be impossible
 with a traditional find-and-replace regexp:
 
 *   Constructing `scoped_ptr<T>` from `NULL`: <https://crbug.com/173286>
 *   Implicit conversions of `scoped_refptr<T>` to `T*`: <https://crbug.com/110610>
 *   Rename everything in Blink to follow Chromium style: <https://crbug.com/563793>
 
 ## Caveats
 
 An invocation of the clang tool runs on one build config. Code that only
 compiles on one platform or code that is guarded by a set of compile-time flags
 can be problematic. Performing a global refactoring typically requires running
 the tool once in each build config with code that needs to be updated.
 
 Other minor issues:
 
 *   Requires a git checkout.
-*   Requires [some hacks to run on Windows](https://codereview.chromium.org/718873004).
 
 ## Prerequisites
 
 A Chromium checkout created with `fetch` should have everything needed.
 
 For convenience, add `third_party/llvm-build/Release+Asserts/bin` to `$PATH`.
 
 ## Writing the tool
 
 LLVM uses C++11 and CMake. Source code for Chromium clang tools lives in
@@ skipping 74 matching lines @@
 Generally, `--tools` should always include `blink_gc_plugin` and `plugins`: otherwise, Chromium won't build.
 
 It is important to use --bootstrap as there appear to be [bugs](https://crbug.com/580745)
 in the clang library this script produces if you build it with gcc, which is the default.
 
 ## Running
 First, build all Chromium targets to avoid failures due to missing dependencies
 that are generated as part of the build:
 
 ```shell
-ninja -C out/Debug
+ninja -C out/Debug  # For non-Windows
+ninja -d keeprsp -C out/Debug  # For Windows
+```
+
+On Windows, generate the compile DB first, and after making any source changes.
+Then omit the `--generate-compdb` in later steps.
+
+```shell
+tools/clang/scripts/generate_win_compdb.py out/Debug
 ```
 
 Then run the actual tool:
 
 ```shell
 tools/clang/scripts/run_tool.py <toolname> \
   --generate-compdb
   out/Debug <path 1> <path 2> ...
 ```
 
@@ skipping 42 matching lines @@
 
 ```shell
 tools/clang/scripts/test_tool.py <tool name>
 ```
 
 The name of the tool binary and the subdirectory for the tool in
 `//tools/clang` must match. The test runner finds all files that match the
 pattern `//tools/clang/<tool name>/tests/*-original.cc`, runs the tool across
 those files, and compared it to the `*-expected.cc` version. If there is a
 mismatch, the result is saved in `*-actual.cc`.