Suppress lint warning "SdCardPath" for getRawAcceptableDirectories()

The following lint warnings are issued every time when chrome/content
shell is built

../../../tmp/tmp6VcHbX/0/MediaResourceGetter.java:365 Do not hardcode "/sdcard/";
 use Environment.getExternalStorageDirectory().getPath() instead: SdCardPath [warning]
        result.add("/mnt/sdcard/");
                   ~~~~~~~~~~~~~~
../../../tmp/tmp6VcHbX/0/MediaResourceGetter.java:366 Do not hardcode "/sdcard/";
 use Environment.getExternalStorageDirectory().getPath() instead: SdCardPath [warning]
        result.add("/sdcard/");
                   ~~~~~~~~~~
../../../tmp/tmp6VcHbX/0/MediaResourceGetter.java:367 Do not hardcode "/data/";
 use Context.getFilesDir().getPath() instead: SdCardPath [warning]
        result.add("/data/data/" + context.getPackageName() + "/cache/");

As these hardcoded values are required and the warnings here are false positives
which are more explained in https://codereview.chromium.org/561743003/#msg5

BUG=None.

Review URL: https://codereview.chromium.org/597283007

Cr-Commit-Position: refs/heads/master@{#296891}

content/public/android/java/src/org/chromium/content/browser/MediaResourceGetter.java

@@ -4,6 +4,7 @@
 
 package org.chromium.content.browser;
 
+import android.annotation.SuppressLint;
 import android.content.Context;
 import android.content.pm.PackageManager;
 import android.media.MediaMetadataRetriever;
@@ -360,6 +361,7 @@ class MediaResourceGetter {
         return info.getType();
     }
 
+    @SuppressLint("SdCardPath")
     private List<String> getRawAcceptableDirectories(Context context) {
         List<String> result = new ArrayList<String>();
         result.add("/mnt/sdcard/");