Tool added to extract network traffic annotations.

tools/clang/traffic_annotation_extractor/README.md

Index: tools/clang/traffic_annotation_extractor/README.md
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+# Traffic Annotation Extrator
+This is a clang tool to extract network traffic annotations. The tool is run by
+`tools/traffic_annotation/traffic_annotaion_auditor`. Refer to it for help on
+how to use.
+
+# Build on Linux
+`tools/clang/scripts/update.py --bootstrap --force-local-build
+   --without-android --extra-tools blink_gc_plugin plugins
+   rewrite_to_chrome_style traffic_annotation_extractor`
+
+# Build on Window
+1. Either open a `VS2015 x64 Native Tools Command Prompt`, or open a normal
+   command prompt and run `depot_tools\win_toolchain\vs_files\
+   $long_autocompleted_hash\win_sdk\bin\setenv.cmd /x64`
+2. Run python `tools/clang/scripts/update.py --bootstrap --force-local-build
+   --without-android --extra-tools blink_gc_plugin plugins
+   rewrite_to_chrome_style traffic_annotation_extractor`
+
+## Usage
+traffic_annotation_extractor -p [build_dir] [file_path] [output_directory]
+Extracts network traffic annotations from |file_path|, based on build parameters
+  in |build_dir|, and writes them as separate files in |output_directory|.
+Each output file will have the following format:
+  - Line 1: File path.
+  - Line 2: Name of the function in which annotation is defined.
+  - Line 3: Line number of annotation.
+  - Line 4: Name of the function that annoation is passed to.
+  - Line 5: Possible errors.
+  - Line 6: Unique id of annotation.
+  - Line 7-: Serialized protobuf of the annotation.