weblayer: fix NPE in CrashReporterController

importMinidumpsCrashKeys may return null. The code was not
handling that.

BUG=1123207
TEST=none

Change-Id: Ibf775a9b053d8c051beb741e43daebc0d3c68fe5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2382876Reviewed-by: Clark DuVall <cduvall@chromium.org>
Commit-Queue: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#803135}

weblayer/browser/java/org/chromium/weblayer_private/CrashReporterControllerImpl.java

@@ -204,6 +204,7 @@ public final class CrashReporterControllerImpl extends ICrashReporterController.
     private String[] processNewMinidumpsOnBackgroundThread() {
         Map<String, Map<String, String>> crashesInfoMap =
                 getCrashFileManager().importMinidumpsCrashKeys();
+        if (crashesInfoMap == null) return new String[0];
         ArrayList<String> localIds = new ArrayList<>(crashesInfoMap.size());
         for (Map.Entry<String, Map<String, String>> entry : crashesInfoMap.entrySet()) {
             JSONObject crashKeysJson = new JSONObject(entry.getValue());