Add ability to select all using keyboard (Ctrl+A) in PDF forms.

pdf/pdfium/pdfium_engine.cc

Index: pdf/pdfium/pdfium_engine.cc
diff --git a/pdf/pdfium/pdfium_engine.cc b/pdf/pdfium/pdfium_engine.cc
index 6d1dacba3d77ec924ae2a1a9185b5e35c0685e1f..f71ef7ce71f8b2ccb87dc7e2326c1967ee9fe648 100644
--- a/pdf/pdfium/pdfium_engine.cc
+++ b/pdf/pdfium/pdfium_engine.cc
@@ -2435,6 +2435,9 @@ bool PDFiumEngine::HasPermission(DocumentPermission permission) const {
 }
 
 void PDFiumEngine::SelectAll() {
+  if (in_form_text_area_)
+    return;
+
   SelectionChangeInvalidator selection_invalidator(this);
 
   selection_.clear();