Make some small tweaks to the build instructions.

docs/ios_build_instructions.md

 # iOS Build Instructions
 
 **See also [the old version of this page](old_ios_build_instructions.md).**
 
 Google employee? See [go/building-chrome](https://goto.google.com/building-chrome) instead.
 
 [TOC]
 
 ## System requirements
 
 * A 64-bit Mac running 10.11+.
 * [Xcode](https://developer.apple.com/xcode) 8.0+.
-* The OSX 10.10 SDK. Run
-  
-      ls `xcode-select -p`/Platforms/MacOSX.platform/Developer/SDKs
+* The OS X 10.10 SDK. Run
+
+    ```shell  
+    $ ls `xcode-select -p`/Platforms/MacOSX.platform/Developer/SDKs
+    ```
  
   to check whether you have it.  Building with the 10.11 SDK works too, but
   the releases currently use the 10.10 SDK.
-* The current version of the JDK (which is required for the Closure compiler).
+* The current version of the JDK (required for the Closure compiler).
 
 ## Install `depot_tools`
 
-Clone the depot_tools repository:
+Clone the `depot_tools` repository:
 
-    $ git clone https://chromium.googlesource.com/chromium/tools/depot_tools.git
+```shell
+$ git clone https://chromium.googlesource.com/chromium/tools/depot_tools.git
+```
 
-Add depot_tools to the end of your PATH (you will probably want to put this
-in your ~/.bashrc or ~/.zshrc). Assuming you cloned depot_tools
-to /path/to/depot_tools:
+Add `depot_tools` to the end of your PATH (you will probably want to put this
+in your `~/.bashrc` or `~/.zshrc`). Assuming you cloned `depot_tools` to
+`/path/to/depot_tools`:
 
-    $ export PATH=$PATH:/path/to/depot_tools
+```shell
+$ export PATH="$PATH:/path/to/depot_tools"
+```
 
 ## Get the code
 
-Create a chromium directory for the checkout and change to it (you can call
+Create a `chromium` directory for the checkout and change to it (you can call
 this whatever you like and put it wherever you like, as
 long as the full path has no spaces):
-    
-    $ mkdir chromium
-    $ cd chromium
 
-Run the `fetch` tool from depot_tools to check out the code and its
+```shell
+$ mkdir chromium && cd chromium
+```
+
+Run the `fetch` tool from `depot_tools` to check out the code and its
 dependencies.
 
-    $ fetch ios
-
-(This is identical to `fetch chromium`, except that it sets `target_os=["ios"]`
-in your `.gclient` file.
+```shell
+$ fetch ios
+```
 
 If you don't want the full repo history, you can save a lot of time by
-adding the `--no-history` flag to fetch. Expect the command to take
-30 minutes on even a fast connection, and many hours on slower ones.
+adding the `--no-history` flag to `fetch`.
 
-When fetch completes, it will have created a directory called `src`.
-The remaining instructions assume you are now in that directory:
+Expect the command to take 30 minutes on even a fast connection, and many
+hours on slower ones.
 
-    $ cd src
+When `fetch` completes, it will have created a hidden `.gclient` file and a
+directory called `src` in the working directory. The remaining instructions
+assume you have switched to the `src` directory:
 
-*Optional*: You can also [install API keys](https://www.chromium.org/developers/how-tos/api-keys)
-if you want to talk to some of the Google services, but this is not necessary
-for most development and testing purposes.
+```shell
+$ cd src
+```
+
+*Optional*: You can also [install API
+keys](https://www.chromium.org/developers/how-tos/api-keys) if you want your
+build to talk to some Google services, but this is not necessary for most
+development and testing purposes.
 
 ## Setting up the build
 
-Since the iOS build is a bit more complicated than a desktop build, we
-provide the `ios/build/tools/setup-gn.py`, which will create four
-appropriately configured build directories under `out` for Release and
-Debug device and simulator builds, and generates an appropriate Xcode
-workspace as well. 
+Since the iOS build is a bit more complicated than a desktop build, we provide
+`ios/build/tools/setup-gn.py`, which will create four appropriately configured
+build directories under `out` for Release and Debug device and simulator
+builds, and generates an appropriate Xcode workspace as well. 
 
 This script is run automatically by fetch (as part of `gclient runhooks`).
 
-You can customize the build by editing the file `$HOME/.setup-gn` (create it
-if it does not exists).  Look at `src/ios/build/tools/setup-gn.config` for
+You can customize the build by editing the file `$HOME/.setup-gn` (create it if
+it does not exist).  Look at `src/ios/build/tools/setup-gn.config` for
 available configuration options.
 
-From this point, you can either build from Xcode or from the command-line
-using `ninja`. The script `setup-gn.py` creates sub-directories named
-`out/${configuration}-${platform}`, so for a `Debug` build for simulator
-use:
+From this point, you can either build from Xcode or from the command line using
+`ninja`. `setup-gn.py` creates sub-directories named
+`out/${configuration}-${platform}`, so for a `Debug` build for simulator use:
 
 ```shell
-ninja -C out/Debug-iphonesimulator gn_all
+$ ninja -C out/Debug-iphonesimulator gn_all
 ```
 
 Note: you need to run `setup-gn.py` script every time one of the `BUILD.gn`
 file is updated (either by you or after rebasing). If you forget to run it,
 the list of targets and files in the Xcode solution may be stale.
 
 You can also follow the manual instructions on the 
-[mac page](mac_build_instructions.md), but make sure you set the
+[Mac page](mac_build_instructions.md), but make sure you set the
 GN arg `target_os="ios"`.
 
 ## Running
 
 Any target that is built and runs on the bots (see [below](#Troubleshooting))
 should run successfully in a local build. As of the time of writing, this is
-only ios_web_shell and unit test targets—see the note at the top of this
-page. Check the bots periodically for updates; more targets (new components)
-will come on line over time.
+only the `ios_web_shell` and `ios_chrome_unittests` targets—see the note at the
+top of this page. Check the bots periodically for updates; more targets (new
+components) will come on line over time.
 
 To run in the simulator from the command line, you can use `iossim`. For
-example, to run a debug build of ios_web_shell:
+example, to run a debug build of `ios_web_shell`:
 
 ```shell
-out/Debug-iphonesimulator/iossim out/Debug-iphonesimulator/ios_web_shell.app
+$ out/Debug-iphonesimulator/iossim out/Debug-iphonesimulator/ios_web_shell.app
 ```
 
 ## Update your checkout
 
 To update an existing checkout, you can run
 
-    $ git rebase-update
-    $ gclient sync
+```shell
+$ git rebase-update
+$ gclient sync
+```
 
 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/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.
 
-The second command syncs the subrepositories to the appropriate versions and
-re-runs the hooks as needed.
+The second command syncs dependencies to the appropriate versions and re-runs
+hooks as needed.
 
 ## Tips, tricks, and troubleshooting
 
-
 If you have problems building, join us in `#chromium` on `irc.freenode.net` and
 ask there. As mentioned above, be sure that the
 [waterfall](http://build.chromium.org/buildbot/waterfall/) is green and the tree
 is open before checking out. This will increase your chances of success.
 
 ### Improving performance of `git status`
 
 `git status` is used frequently to determine the status of your checkout.  Due
-to the number of files in Chromium's checkout, `git status` performance can be
-quite variable.  Increasing the system's vnode cache appears to help.  By
-default, this command:
+to the large number of files in Chromium's checkout, `git status` performance
+can be quite variable.  Increasing the system's vnode cache appears to help.
+By default, this command:
 
-    sysctl -a | egrep kern\..*vnodes
+```shell
+$ sysctl -a | egrep kern\..*vnodes
+```
 
 Outputs `kern.maxvnodes: 263168` (263168 is 257 * 1024).  To increase this
 setting:
 
-    sudo sysctl kern.maxvnodes=$((512*1024))
+```shell
+$ sudo sysctl kern.maxvnodes=$((512*1024))
+```
 
 Higher values may be appropriate if you routinely move between different
 Chromium checkouts.  This setting will reset on reboot, the startup setting can
 be set in `/etc/sysctl.conf`:
 
-    echo kern.maxvnodes=$((512*1024)) | sudo tee -a /etc/sysctl.conf
+```shell
+$ echo kern.maxvnodes=$((512*1024)) | sudo tee -a /etc/sysctl.conf
+```
 
 Or edit the file directly.
 
-If your `git --version` reports 2.6 or higher, the following may also improve
+If `git --version` reports 2.6 or higher, the following may also improve
 performance of `git status`:
 
-    git update-index --untracked-cache
+```shell
+$ git update-index --untracked-cache
+```
 
 ### Xcode license agreement
 
 If you're getting the error
 
-```
-Agreeing to the Xcode/iOS license requires admin privileges, please re-run as root via sudo.
-```
+> Agreeing to the Xcode/iOS license requires admin privileges, please re-run as
+> root via sudo.
 
 the Xcode license hasn't been accepted yet which (contrary to the message) any
 user can do by running:
 
-    xcodebuild -license
+```shell
+$ xcodebuild -license
+```
 
 Only accepting for all users of the machine requires root:
 
-    sudo xcodebuild -license
+```shell
+$ sudo xcodebuild -license
+```