[Android] Add StrictModeContext.allowSlowCalls()

This CL adds StrictModeContext.allowSlowCalls() to avoid crashes when
non-Chrome code calls StrictMode.noteSlowCall(). Use sparingly (e.g.,
to avoid crashes on older versions of the library if a new version
no longer calls noteSlowCall).

Bug: 793841
Change-Id: I24a03b8c241499c00a871a564cff0a5b0b58a87a
Reviewed-on: https://chromium-review.googlesource.com/824273Reviewed-by: Yaron Friedman <yfriedman@chromium.org>
Commit-Queue: Boris Sazonov <bsazonov@chromium.org>
Cr-Commit-Position: refs/heads/master@{#523777}

base/android/java/src/org/chromium/base/StrictModeContext.java

@@ -63,6 +63,16 @@ public final class StrictModeContext implements Closeable {
         return new StrictModeContext(oldPolicy);
     }
 
+    /**
+     * Convenience method for disabling StrictMode for slow calls with try-with-resources.
+     */
+    public static StrictModeContext allowSlowCalls() {
+        StrictMode.ThreadPolicy oldPolicy = StrictMode.getThreadPolicy();
+        StrictMode.setThreadPolicy(
+                new StrictMode.ThreadPolicy.Builder(oldPolicy).permitCustomSlowCalls().build());
+        return new StrictModeContext(oldPolicy);
+    }
+
     @Override
     public void close() {
         if (mThreadPolicy != null) {