Fix findbugs warnings from https://codereview.chromium.org/406023002/

It was rebased incorrectly and the new findbugs (from a move) weren't added.
BUG=398263
R=boliu@chromium.org
TBR=boliu

Review URL: https://codereview.chromium.org/544303002

Cr-Commit-Position: refs/heads/master@{#293564}

build/android/findbugs_filter/findbugs_known_bugs.txt

@@ -22,3 +22,5 @@ M V EI: org.chromium.chrome.browser.ChromeBrowserProvider$BookmarkNode.thumbnail
 M M LI: Incorrect lazy initialization of static field org.chromium.chrome.browser.sync.ProfileSyncService.sSyncSetupManager in org.chromium.chrome.browser.sync.ProfileSyncService.get(Context)  At ProfileSyncService.java
 M V EI: org.chromium.android_webview.AwWebResourceResponse.getResponseHeaderNames() may expose internal representation by returning AwWebResourceResponse.mResponseHeaderNames  At AwWebResourceResponse.java
 M V EI: org.chromium.android_webview.AwWebResourceResponse.getResponseHeaderValues() may expose internal representation by returning AwWebResourceResponse.mResponseHeaderValues  At AwWebResourceResponse.java
+M V EI2: org.chromium.content_public.browser.LoadUrlParams.setPostData(byte[]) may expose internal representation by storing an externally mutable object into LoadUrlParams.mPostData  At LoadUrlParams.java
+M V EI: org.chromium.content_public.browser.LoadUrlParams.getPostData() may expose internal representation by returning LoadUrlParams.mPostData  At LoadUrlParams.java