Fix MediaRouter.getInstance StrictMode error

Some manufacturers have a native MediaRouter implementations that causes
a StrictModeDiskReadViolation when trying to acquire a MediaRouter
instance.

This CL temporarily changes the StrictMode policy to allow disk reads
when we acquire the native MediaRouter.

Bug: 818325
Change-Id: I2b1452c03ef6767d17c243ce5e9c4964cb95c75d
Reviewed-on: https://chromium-review.googlesource.com/947542Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Commit-Queue: Thomas Guilbert <tguilbert@chromium.org>
Cr-Commit-Position: refs/heads/master@{#541262}

chrome/android/java/src/org/chromium/chrome/browser/media/router/ChromeMediaRouter.java

@@ -8,6 +8,7 @@ import android.support.v7.media.MediaRouter;
 
 import org.chromium.base.ContextUtils;
 import org.chromium.base.Log;
+import org.chromium.base.StrictModeContext;
 import org.chromium.base.SysUtils;
 import org.chromium.base.VisibleForTesting;
 import org.chromium.base.annotations.CalledByNative;
@@ -98,7 +99,10 @@ public class ChromeMediaRouter implements MediaRouteManager {
     @Nullable
     public static MediaRouter getAndroidMediaRouter() {
         if (sAndroidMediaRouterSetForTest) return sAndroidMediaRouterForTest;
-        try {
+
+        // Some manufacturers have an implementation that causes StrictMode
+        // violations. See https://crbug.com/818325.
+        try (StrictModeContext unused = StrictModeContext.allowDiskReads()) {
             // Pre-MR1 versions of JB do not have the complete MediaRouter APIs,
             // so getting the MediaRouter instance will throw an exception.
             return MediaRouter.getInstance(ContextUtils.getApplicationContext());