AW: use ScalableTimeout for tests

This changes AwActivityTestRule to use ScalableTimeout instead of
hardcoding the timeout. This should have no effect (bots don't appear to
set this value), but gives devs the option of scaling the timeout if
they use tools like valgrind.

Bug: 1013465
Test: N/A
Change-Id: I05100f36a96cb21ac989c7c5e1f12abbaca16ffc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1861048Reviewed-by: Andrew Luo <aluo@chromium.org>
Reviewed-by: Tao Bai <michaelbai@chromium.org>
Auto-Submit: Nate Fischer <ntfschr@chromium.org>
Commit-Queue: Nate Fischer <ntfschr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#706056}

android_webview/javatests/src/org/chromium/android_webview/test/AwActivityTestRule.java

@@ -4,6 +4,8 @@
 
 package org.chromium.android_webview.test;
 
+import static org.chromium.base.test.util.ScalableTimeout.scaleTimeout;
+
 import android.content.Context;
 import android.support.test.InstrumentationRegistry;
 import android.support.test.rule.ActivityTestRule;
@@ -46,7 +48,7 @@ import java.util.regex.Pattern;
 
 /** Custom ActivityTestRunner for WebView instrumentation tests */
 public class AwActivityTestRule extends ActivityTestRule<AwTestRunnerActivity> {
-    public static final long WAIT_TIMEOUT_MS = 15000L;
+    public static final long WAIT_TIMEOUT_MS = scaleTimeout(15000L);
 
     public static final int CHECK_INTERVAL = 100;