Setting up the environment for Visual Studio 2013
You must build with Visual Studio 2013 Update 4, no other versions are supported.
You must have Windows 7 x64 or later. x86 OSs are unsupported.
Step 2: Follow the appropriate path below:
Run set DEPOT_TOOLS_WIN_TOOLCHAIN=0, or set that variable in your global environment.
Note that Visual Studio Express is not supported and will not be able to build Chromium.
Run: download_from_google_storage --config and follow the authentication instructions. Note that you must authenticate with your @google.com credentials, not @chromium.org.
Once you've done this, the toolchain will be installed automatically for you in Step 3, below (near the end of the step).
The toolchain will be in depot_tools\win_toolchain, and windbg can be found in depot_tools\win_toolchain\vs2013_files\win8sdk\Debuggers.
If you want the IDE for debugging and editing, you will need to install it separately, but this is optional and not needed to build Chromium.
Step 4: ninja -C out\Debug chrome
If you're primarily going to be doing debug dev builds, you'll want to set GYP_DEFINES=component=shared_library, which uses a DLL build and incremental linking, which makes linking much faster in Debug.