Shift-Click doesn't extend selection in internal PDF plugin

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 c4e703efe65e47a20f9820b1c788d4c4add59681..4105f69b3269d3ea5ee7289e557476e7f569f634 100644
--- a/pdf/pdfium/pdfium_engine.cc
+++ b/pdf/pdfium/pdfium_engine.cc
@@ -600,7 +600,8 @@ PDFiumEngine::PDFiumEngine(PDFEngine::Client* client)
       called_do_document_action_(false),
       render_grayscale_(false),
       progressive_paint_timeout_(0),
-      getting_password_(false) {
+      getting_password_(false),
+      last_char_index_(-1) {
   find_factory_.Initialize(this);
   password_factory_.Initialize(this);
 
@@ -1693,6 +1694,7 @@ bool PDFiumEngine::OnMouseDown(const pp::MouseInputEvent& event) {
     return true;
   }
 
+  int last_page_index = last_page_mouse_down_;
   if (page_index != -1) {
     last_page_mouse_down_ = page_index;
     double page_x, page_y;
@@ -1715,6 +1717,15 @@ bool PDFiumEngine::OnMouseDown(const pp::MouseInputEvent& event) {
   }
 
   client_->FormTextFieldFocusChange(false);
+  if (event.GetModifiers() == (PP_INPUTEVENT_MODIFIER_LEFTBUTTONDOWN |
+                               PP_INPUTEVENT_MODIFIER_SHIFTKEY) &&
+      event.GetClickCount() == 1) {
+    HandleShiftClick(last_page_index, page_index, char_index);
+    last_char_index_ = char_index;
+    return true;
+  }
+
+  last_char_index_ = char_index;
 
   if (area != PDFiumPage::TEXT_AREA)
     return true;  // Return true so WebKit doesn't do its own highlighting.
@@ -3469,6 +3480,55 @@ void PDFiumEngine::RotateInternal() {
   }
 }
 
+void PDFiumEngine::HandleShiftClick(const int last_page_index,
+                                    const int page_index,
+                                    const int char_index) {
+  selecting_ = true;
+  if (last_page_index == -1 || last_page_index == page_index) {
+    if (last_char_index_ != -1) {
+      if (char_index == -1) {
+        selection_.push_back(
+            PDFiumRange(pages_[page_index], 0, last_char_index_ + 1));
+      } else {
+        if (char_index > last_char_index_) {
+          selection_.push_back(PDFiumRange(pages_[page_index], last_char_index_,
+                                           char_index - last_char_index_ + 1));
+        } else if (char_index < last_char_index_) {
+          selection_.push_back(PDFiumRange(pages_[page_index], char_index,
+                                           last_char_index_ - char_index + 1));
+        }
+      }
+    } else {
+      if (char_index != -1)
+        selection_.push_back(
+            PDFiumRange(pages_[page_index], 0, char_index + 1));
+    }
+  } else {
+    if (last_char_index_ != -1 && char_index != -1) {
+      if (last_page_index < page_index) {
+        selection_.push_back(
+            PDFiumRange(pages_[last_page_index], last_char_index_,
+                        pages_[last_page_index]->GetCharCount()));
+        for (int i = last_page_index + 1; i < page_index; i++) {
+          selection_.push_back(
+              PDFiumRange(pages_[i], 0, pages_[i]->GetCharCount()));
+        }
+        selection_.push_back(
+            PDFiumRange(pages_[page_index], 0, char_index + 1));
+      } else {
+        selection_.push_back(PDFiumRange(pages_[page_index], char_index,
+                                         pages_[page_index]->GetCharCount()));
+        for (int i = page_index + 1; i < last_page_index; i++) {
+          selection_.push_back(
+              PDFiumRange(pages_[i], 0, pages_[i]->GetCharCount()));
+        }
+        selection_.push_back(
+            PDFiumRange(pages_[last_page_index], 0, last_char_index_ + 1));
+      }
+    }
+  }
+}
+
 void PDFiumEngine::Form_Invalidate(FPDF_FORMFILLINFO* param,
                                    FPDF_PAGE page,
                                    double left,