Docs: fix documentation for java_cpp_strings

No change to logic, only docs.

This fixes several mistakes in the java_cpp_strings docs:
 * Do not need GENERATED_JAVA_PACKAGE
 * {NATIVE_STRINGS}, not {NATIVE_SWITCHES}
 * Do not need "This file is autogenerated..." boilerplate in the
   template
 * Consistent package name between template and generated file
 * Consistent class name between template and generated file
 * Change {YEAR} to $YEAR, as this must not be left templated, but
   should be filled in by the author

This also adds some more opinionated changes:
 * Mark the class as "public final" not "public abstract" and mark the
   constructor private, as this is a more robust way to mark the class
   as non-instantiable
 * Include the boilerplate "This following string constants..." [sic]
   message in the generated file, as that's what the script inserts.
 * Use more realistic file names (foo_switches.cc and FooSwitches.java).
 * Add javadoc for the template file, as a suggestion for others to
   document the generated class.

Bug: 1011991
Test: tools/md_browser/md_browser.py
Test: Upload to gerrit > open file > click "gitiles"
Change-Id: Ia1aa96cf50842bf226f35440fd2cafe8a186f8b5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1863866Reviewed-by: Ian Vollick <vollick@chromium.org>
Commit-Queue: Nate Fischer <ntfschr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#706456}

docs/android_accessing_cpp_switches_in_java.md

@@ -11,76 +11,82 @@ specified in a comment within the switch file itself.
 
 ## Usage
 
-1. Add directives to your C++ switch file
-
-    ```cpp
-    // GENERATED_JAVA_PACKAGE: org.chromium.chrome
-
-    // ...snip...
-
-    // Documentation for the following switch.
-    const char kSomeSwitch[] = "some-switch";
-
-    // ...snip...
-    ```
-
-2. Create a template file
+1. Create a template file (ex. `FooSwitches.java.tmpl`)
    ```java
-    // Copyright {YEAR} The Chromium Authors. All rights reserved.
+    // Copyright $YEAR The Chromium Authors. All rights reserved.
     // Use of this source code is governed by a BSD-style license that can be
     // found in the LICENSE file.
 
-    // This file is autogenerated by
-    //     {SCRIPT_NAME}
-    // From
-    //     {SOURCE_PATH}, and
-    //     {TEMPLATE_PATH}
-
-    package my.java.package
+    package org.chromium.foo;
 
     // Be sure to escape any curly braces in your template by doubling as
     // follows.
-    public abstract class MySwitches {{
+    /**
+     * Contains command line switches that are specific to the foo project.
+     */
+    public final class FooSwitches {{
 
-    {NATIVE_SWITCHES}
+    {NATIVE_STRINGS}
 
+        // Prevents instantiation.
+        private FooSwitches() {{}}
     }}
    ```
 
-3. Add a new build target
+2. Add a new build target
 
     ```gn
     import("//build/config/android/rules.gni")
 
-    java_cpp_strings("foo_generated_switch") {
+    java_cpp_strings("java_switches") {
       sources = [
-        "//base/android/native_foo_switches.cc",
+        "//base/android/foo_switches.cc",
       ]
-      template = "//base/android/java_templates/MySwitches.java.tmpl"
+      template = "//base/android/java_templates/FooSwitches.java.tmpl"
     }
     ```
 
-5. Add the new target to the desired android_library targets srcjar_deps:
+3. Add the new target to the desired `android_library` targets `srcjar_deps`:
 
     ```gn
     android_library("base_java") {
       srcjar_deps = [
-        ":foo_generated_switches",
+        ":java_switches",
       ]
     }
     ```
 
-5. The generated file `org/chromium/chrome/NativeFooSwitches.java` would contain:
+4. The generated file `out/Default/gen/.../org/chromium/foo/FooSwitches.java`
+   would contain:
 
     ```java
-    package org.chromium.chrome;
+    // Copyright $YEAR The Chromium Authors. All rights reserved.
+    // Use of this source code is governed by a BSD-style license that can be
+    // found in the LICENSE file.
+
+    package org.chromium.foo;
+
+    /**
+     * Contains command line switches that are specific to the foo project.
+     */
+    public final class FooSwitches {
 
-    public final class NativeFooSwitches {
         // ...snip...
 
+        // This following string constants were inserted by
+        //     java_cpp_strings.py
+        // From
+        //     ../../base/android/foo_switches.cc
+        // Into
+        //     ../../base/android/java_templates/FooSwitches.java.tmpl
+
+        // Documentation for the C++ switch is copied here.
         public static final String SOME_SWITCH = "some-switch";
 
         // ...snip...
+
+        // Prevents instantiation.
+        private FooSwitches() {}
     }
     ```