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This is a Markdown conversion of https://www.chromium.org/developers/coding-style

This separates out the language-independent parts from the C++-specific parts.

The C++ portion is mostly the same as the web page with the following updates:
 - New stuff at the top that references clang format and style update process.
 - The sections on ?: and function parameter ordering were deleted. The advice was long and detailed and seems to contradict Clang format.
 - Converted scoped_ptr to unique_ptr
 - Removed the one-line section on return values vs out params as it didn't seem to add much.
 - Removed the list of platform-specific ifdefs. Some were out-of-date, and "use the ones from build_config.h" seems sufficient for the style guide.

Review-Url: https://codereview.chromium.org/2127713004
Cr-Commit-Position: refs/heads/master@{#403954}