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/fpdfsdk/include/cpdfsdk_baannot.h b/fpdfsdk/include/cpdfsdk_baannot.h
index e83cb0f..0f41738 100644
--- a/fpdfsdk/include/cpdfsdk_baannot.h
+++ b/fpdfsdk/include/cpdfsdk_baannot.h
@@ -37,6 +37,7 @@
                     CPDF_RenderOptions* pOptions) override;
 
   CPDF_Dictionary* GetAnnotDict() const;
+  CPDF_Annot* GetPDFPopupAnnot() const;
 
   void SetContents(const CFX_WideString& sContents);
   CFX_WideString GetContents() const;
@@ -96,6 +97,8 @@
                        const CFX_ByteString& sContents,
                        const CFX_ByteString& sAPState = "");
 
+  void SetOpenState(bool bState);
+
  protected:
   CPDF_Annot* m_pAnnot;
 };