Display content of the annotation when mouse hover.

Each annotation has its contents, and users should be able to see the
contents. In this patch, PDFium creates a Popup annotation for each
annotation and stores the author and the content. When a user mouse
hover on the annotation, PDFium draws the corresponding Popup annotation
and displays the content.

Also, roll DEPS for testing/corpus to 5867fa6.

BUG=62625

Review-Url: https://codereview.chromium.org/2273893002
diff --git a/testing/SUPPRESSIONS b/testing/SUPPRESSIONS
index f97e38c..49c9970 100644
--- a/testing/SUPPRESSIONS
+++ b/testing/SUPPRESSIONS
@@ -281,6 +281,9 @@
 all_trigger_print.pdf * * *
 all_trigger_run_js_lunchurl.pdf mac * *
 all_trigger_run_js_maildoc.pdf mac * *
+annotation_highlight_author_content.pdf mac * *
+annotation_highlight_long_content.pdf mac * *
+annotation_highlight_no_author.pdf mac * *
 app_launchurl.pdf mac * *
 appstoredescription3.1_en_updated.pdf mac * *
 bookmark.pdf * * *