Improve development workflow with built libchromiumcontent

- Add `--debug_libchromiumcontent` to build libchromiumcontent for debugging
  (shared library build).
- By default, only invoke `gclient sync` the first time to checkout chromium
  source tree. Add `--force_update_libchromiumcontent` switch to force updating.
- Document new options.

The goal is to allow faster edit/compile cycles when debugging/making changes
to libchromiumcontent.

docs/development/build-instructions-linux.md

@@ -156,15 +156,10 @@ To avoid using the prebuilt binaries of `libchromiumcontent`, you can build `lib
   ```bash
   $ git submodule update --init --recursive
   ```
-  4. Copy the .gclient config file
+  4. Pass the `--build_release_libcc` switch to `bootstrap.py` script:
 
   ```bash
-  $ cp vendor/libchromiumcontent/.gclient .
-  ```
-  5. Pass the `--build_libchromiumcontent` switch to `bootstrap.py` script:
-
-  ```bash
-  $ ./script/bootstrap.py -v --build_libchromiumcontent
+  $ ./script/bootstrap.py -v --build_release_libcc
   ```
 
 Note that by default the `shared_library` configuration is not built, so you can
@@ -186,7 +181,7 @@ in `<path>/bin/`.
 For example if you installed `clang` under `/user/local/bin/clang`:
 
 ```bash
-$ ./script/bootstrap.py -v --build_libchromiumcontent --clang_dir /usr/local
+$ ./script/bootstrap.py -v --build_release_libcc --clang_dir /usr/local
 $ ./script/build.py -c R
 ```
 
@@ -199,7 +194,7 @@ variables to the ones you want.
 For example building with GCC toolchain:
 
 ```bash
-$ env CC=gcc CXX=g++ ./script/bootstrap.py -v --build_libchromiumcontent --disable_clang
+$ env CC=gcc CXX=g++ ./script/bootstrap.py -v --build_release_libcc --disable_clang
 $ ./script/build.py -c R
 ```
 
@@ -223,4 +218,4 @@ custom the building configurations:
 * `LDFLAGS`
 
 The environment variables have to be set when executing the `bootstrap.py`
-script, it won't work in the `build.py` script.
+script, it won't work in the `build.py` script.