Speculative fix for nullptr crash in calculateSignalLevel

The crash only happens on certain devices in certain countries.
The crash trace seems to indicate that the context could be null
in some cases.

Change-Id: I0ad8bdd4c79e66f7eebaf269154b9852e48e787f
Bug: 1019974
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1892062Reviewed-by: Ryan Sturm <ryansturm@chromium.org>
Reviewed-by: Paul Jensen <pauljensen@chromium.org>
Commit-Queue: Tarun Bansal <tbansal@chromium.org>
Cr-Commit-Position: refs/heads/master@{#711414}

net/android/java/src/org/chromium/net/AndroidNetworkLibrary.java

@@ -255,6 +255,14 @@ class AndroidNetworkLibrary {
      */
     @CalledByNative
     public static int getWifiSignalLevel(int countBuckets) {
+        // Some devices unexpectedly have a null context. See https://crbug.com/1019974.
+        if (ContextUtils.getApplicationContext() == null) {
+            return -1;
+        }
+        if (ContextUtils.getApplicationContext().getContentResolver() == null) {
+            return -1;
+        }
+
         Intent intent = null;
         try {
             intent = ContextUtils.getApplicationContext().registerReceiver(