[WebView] Fix the run_tests.sh script and add documentation.

android_webview/tools/system_webview_shell/test/data/run_tests.sh

Index: android_webview/tools/system_webview_shell/test/data/run_tests.sh
diff --git a/android_webview/tools/system_webview_shell/test/data/run_tests.sh b/android_webview/tools/system_webview_shell/test/data/run_tests.sh
index e017a505d6e8520b80eef314ce7109736bbe1bab..442da03d4c0d3715d9100263debfa4a00373d1cd 100755
--- a/android_webview/tools/system_webview_shell/test/data/run_tests.sh
+++ b/android_webview/tools/system_webview_shell/test/data/run_tests.sh
@@ -4,15 +4,32 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+# How to use:
+#
+# 1. Build system_webview_shell_apk system_webview_apk (or
+#    system_webview_google_apk for non AOSP devices) and
+#    system_webview_shell_layout_test_apk.
+# 2. Install the shell and system_webview on the device
+#    (e.g. adb install -r -d out/Debug/apks/SystemWebView.apk)
+#    and make sure it is enabled.

[Torne, 2017/01/30 14:27:22]

Isn't the intention of the autogenerated scripts to handle these kinds of steps
for us?

[timvolodine, 2017/02/04 02:42:22]

right, this is a bit elaborate I'll double-check what the wrapper script does
exactly. However some initial install has to happen anyway for it to work on a
new device.

+# 3. Update the build output directory SCRIPT_BUILD_DIR below
+#    if different.
+# 3. Execute run_test.sh [rebaseline]
+#    Simply running this script is equivalent to running the
+#    tests in WebViewLayoutTest. With the [rebaseline] argument
+#    the script will produce a shadow test_rebaseline/ directory
+#    with the new rebased expectation files.
+#
+
+# if necessary update this to reflect the output build directory.
+SCRIPT_BUILD_DIR="../../../../../out/Debug/"

[Torne, 2017/01/30 14:27:22]

I don't think it's reasonable to hardcode this output directory - now that we
have gn most people don't use out/Debug (at least I don't) and there's no
particular required directory location.

Shouldn't we instead be making the generated script do all the right stuff to
run the tests, and getting rid of this script? Or am I not understanding the
test setup?

[timvolodine, 2017/02/04 02:42:22]

good point, so maybe just have a parameter (with out/Debug as default)
so, this script has the ability to do some rebaselining for the 'layout' tests
expectations, which is kind of 'special' in this case. As I understand it the
generated scripts are purely for running the tests similar to what
test_runner.py used to do..

+
 PACKAGE_NAME="org.chromium.webview_shell.test"
 DEVICE_WEBVIEW_TEST_PATH="/sdcard/chromium_tests_root/android_webview/tools/"
 DEVICE_WEBVIEW_TEST_PATH+="system_webview_shell/test/data/"
-TESTRUNNER="../../../../build/android/test_runner.py"
+RUNNER=$SCRIPT_BUILD_DIR"bin/run_system_webview_shell_layout_test_apk"
 
-$TESTRUNNER instrumentation \
-    --test-apk SystemWebViewShellLayoutTest \
-    -f 'WebViewLayoutTest*' \
-    --isolate-file-path android_webview/system_webview_shell_test_apk.isolate
+$RUNNER
 
 if [ "$1" = "rebaseline" ]; then
   adb shell am instrument -w -e mode rebaseline -e class \