AW: comment to explain StaticFieldLeak warning

No change to behavior, this only adds a comment.

This adds a comment explaining why we're going to ignore the
StaticFieldLeak lint warning. There is no real leak because the task
doesn't run for a long time.

Bug: 804422
Test: N/A
Change-Id: I5a70a04a4eb5eed748f20a2396ea8dad3b86770c
Reviewed-on: https://chromium-review.googlesource.com/942029Reviewed-by: Richard Coles <torne@chromium.org>
Commit-Queue: Nate Fischer <ntfschr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#539975}

android_webview/java/src/org/chromium/android_webview/AwWebContentsDelegateAdapter.java

@@ -333,6 +333,8 @@ class AwWebContentsDelegateAdapter extends AwWebContentsDelegate {
         final int mRenderId;
         final int mModeFlags;
         final String[] mFilePaths;
+
+        // The task doesn't run long, so we don't gain anything from a weak ref.
         @SuppressLint("StaticFieldLeak")
         final Context mContext;