crazylinker: fix java tests and add a doc

I found that crazylinker tests are special enough not to be run during
regular testing. I fixed a small issue and added a document about a few
non-trivial-to-discover ways to test the crazylinker in Chromium
checkout.

After the fix all the off-CQ testing described in the doc passes on my
Nexus5X, with the exception of fuzzers - I did not run those.

Applying TBR for docs only.

TBR=rmcilroy@chromium.org

Bug: 981599
Change-Id: I7ead0ef59c6b402729393ba273798107afefed46
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1695309Reviewed-by: Egor Pasko <pasko@chromium.org>
Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Reviewed-by: Benoit L <lizeb@chromium.org>
Commit-Queue: Egor Pasko <pasko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#676528}

base/android/java/src/org/chromium/base/library_loader/Linker.java

@@ -269,7 +269,7 @@ public abstract class Linker {
         assertLinkerTestsAreEnabled();
 
         synchronized (sLock) {
-            sSingleton.mTestRunnerClassName = testRunnerClassName;
+            Linker.getInstance().mTestRunnerClassName = testRunnerClassName;
         }
     }
 

build/android/pylib/linker/test_case.py

@@ -27,11 +27,7 @@
        Host-driven tests have also been tried, but since they're really
        sub-classes of instrumentation tests, they didn't work well either.
 
-   To build and run the linker tests, do the following:
-
-     ninja -C out/Debug chromium_linker_test_apk
-     out/Debug/bin/run_chromium_linker_test_apk
-
+   To build and run, refer to android_linker_testing.md.
 """
 # pylint: disable=R0201
 

third_party/android_crazy_linker/BUILD.gn

@@ -9,6 +9,9 @@ import("//testing/test.gni")
 # NOTE: This file is included in Linux builds to build the
 # crazy_linker_zip_fuzzer target (see below). However, the rest of the
 # crazy linker doesn't build or work on Linux yet.
+#
+# NOTE: Instructions for testing the crazy linker are in
+# android_linker_testing.md.
 
 config("crazy_config") {
   include_dirs = [ "src/include" ]

third_party/android_crazy_linker/README.chromium

@@ -100,4 +100,6 @@ Local Modifications:
 
 - Improve FileDescriptor class.
 
-- Safer zip parsing code (avoid integer overflows and add range checks).
\ No newline at end of file
+- Safer zip parsing code (avoid integer overflows and add range checks).
+
+- Add a document about testing the crazy linker in a Chromium checkout

third_party/android_crazy_linker/src/README.TXT

@@ -125,9 +125,6 @@ BUGS & TODOs:
 Testing:
 --------
 
-  If you modify this code, check your changes by running the test suite using:
-
-    cd $NDK
-    tests/run-tests.sh crazy_linker
+  See android_linker_testing.md
 
   See DESIGN.TXT for an overview of the library's design.

third_party/android_crazy_linker/src/android_linker_testing.md

+# Testing the Android Crazy Linker
+
+The crazy linker is a custom dynamic linker used by Chrome on older Android
+versions where dynamic linking is not as advanced. It provides
+`android_dlopen_ext` functionality, RELRO sharing, compressed relocations, etc.
+
+For crazy reasons outlined in `linker/test_case.py` this linker cannot be tested
+using GTest or instrumentation test, hence it also carries a custom testing
+framework. The tests are not run as part of CQ, but it is still desirable to run
+them before landing changes in code locations listed below.
+
+Sorry.
+
+These instructions assume
+[Building Chromium for Android](android_build_instructions.md) as a
+prerequisite.
+
+## Code Locations
+
+The tested functionality is spread across these locations:
+```
+third_party/android_crazy_linker
+base/android/java/src/org/chromium/base/library_loader
+```
+
+The tests themselves are living mostly in these places:
+```
+build/android/pylib/linker/test_case.py
+content/shell/android
+```
+
+## Running native tests
+
+This will run both unittests and regression tests:
+```
+autoninja -C out/Release android_crazy_linker_tests
+out/Release/bin/run_android_crazy_linker_tests --unit-tests
+```
+
+Verbosity of the output can be increased by setting `CRAZY_DEBUG` to 1 in
+`crazy_linker_debug.h`.
+
+## Running Java Tests
+
+We recommend running these tests in Release mode, as there are known
+complications in testing with the component build. Setting `Linker.DEBUG` to
+`true` should also help increase verbosity of the output.
+```
+autoninja -C out/Release chromium_linker_test_apk
+out/Release/bin/run_chromium_linker_test_apk
+```
+
+## Fuzzer Tests
+
+There are also a few tests for fuzzing the ZIP parser. The instructions to run
+them are at the bottom of `third_party/android_crazy_linker/BUILD.gn`.