Update URLs in docs; replace some uses of 'master'

Bug: 1231155
Change-Id: I0634229c0739c97ac0d7530dd58c33771958149a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3042058
Reviewed-by: Toby Huang <tobyhuang@chromium.org>
Commit-Queue: Andrew Williams <awillia@google.com>
Cr-Commit-Position: refs/heads/master@{#903745}
diff --git a/docs/windows_build_instructions.md b/docs/windows_build_instructions.md
index 370e9be..f975bfc 100644
--- a/docs/windows_build_instructions.md
+++ b/docs/windows_build_instructions.md
@@ -167,7 +167,7 @@
 ## Setting up the build
 
 Chromium uses [Ninja](https://ninja-build.org) as its main build tool along with
-a tool called [GN](https://gn.googlesource.com/gn/+/master/docs/quick_start.md)
+a tool called [GN](https://gn.googlesource.com/gn/+/main/docs/quick_start.md)
 to generate `.ninja` files. You can create any number of *build directories*
 with different configurations. To create a build directory:
 
@@ -185,7 +185,7 @@
   The default will be a debug component build matching the current host
   operating system and CPU.
 * For more info on GN, run `gn help` on the command line or read the [quick
-  start guide](https://gn.googlesource.com/gn/+/master/docs/quick_start.md).
+  start guide](https://gn.googlesource.com/gn/+/main/docs/quick_start.md).
 
 ### Faster builds
 
@@ -387,9 +387,9 @@
 ```
 
 The first command updates the primary Chromium source repository and rebases
-any of your local branches on top of tip-of-tree (aka the Git branch `origin/master`).
-If you don't want to use this script, you can also just use `git pull` or
-other common Git commands to update the repo.
+any of your local branches on top of tip-of-tree (aka the Git branch
+`origin/main`). If you don't want to use this script, you can also just use
+`git pull` or other common Git commands to update the repo.
 
 The second command syncs the subrepositories to the appropriate versions,
 deleting those that are no longer needed, and re-runs the hooks as needed.