Add a clang tool to detect std::move(raw ptr)

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:
 
@@ skipping 92 matching lines @@
 Running this command builds the [Oilpan plugin](https://chromium.googlesource.com/chromium/src/+/master/tools/clang/blink_gc_plugin/),
 the [Chrome style
 plugin](https://chromium.googlesource.com/chromium/src/+/master/tools/clang/plugins/),
 and the [Blink to Chrome style rewriter](https://chromium.googlesource.com/chromium/src/+/master/tools/clang/rewrite_to_chrome_style/). Additional arguments to `--extra-tools` should be the name of
 subdirectories in
 [//tools/clang](https://chromium.googlesource.com/chromium/src/+/master/tools/clang).
 
 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.
 
+Once clang is bootsrapped, incremental builds can be done by invoking `ninja` in
+the `third_party/llvm-build/Release+Asserts` directory. In particular,
+recompiling solely the tool you are writing can be accomplished by executing
+`ninja rewrite_to_chrome_style` (replace `rewrite_to_chrome_style` with your
+tool's name).
+
 ## 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  # For non-Windows
 ninja -d keeprsp -C out/Debug  # For Windows
 
 # experimental alternative:
 $gen_targets = $(ninja -C out/gn -t targets all \
@@ skipping 80 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`.