🍱 Add example regex for Java test DEPS.

Java tests are split into unit and instrumentation tests, which will
require different dependencies. Previously these tests lived in
different directories, but with modularisation they will live alongside
each other.

It seems reasonable change the naming convention to *Test.java for
instrumentation tests and UnitTest.java for unit tests. This change
provides an example in the checkdeps README of specific_include_rules
with the correct regular expressions to provide different DEPS for
unit and instrumentation tests.

Change-Id: Ia3c49c3d82100a3c9404d5b663cc1a8998e8bb59
Bug: 1164866
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2648674
Reviewed-by: Thomas Anderson <thomasanderson@chromium.org>
Commit-Queue: Peter Conn <peconn@chromium.org>
Cr-Commit-Position: refs/heads/master@{#847523}

buildtools/checkdeps/README.md

@@ -59,6 +59,20 @@ specific_include_rules = {
 }
 ```
 
+To add different dependencies for Java instrumentation and unit tests, the
+following regular expressions may be useful:
+
+```
+specific_include_rules = {
+  '.*UnitTest\.java': [
+    # Rules for unit tests.
+  ],
+  '.*(?<!Unit)Test\.java': [
+    # Rules for instrumentation tests.
+  ],
+}
+```
+
 You can optionally ignore the rules inherited from parent directories, similar
 to "set noparent" in OWNERS files. For example, adding `noparent = True` in
 //ash/components/DEPS will cause rules from //ash/DEPS to be ignored, thereby