Enable PDF accessibility when RenderFrame's accessibility mode changes.

components/pdf/renderer/pdf_accessibility_tree.cc

Index: components/pdf/renderer/pdf_accessibility_tree.cc
diff --git a/components/pdf/renderer/pdf_accessibility_tree.cc b/components/pdf/renderer/pdf_accessibility_tree.cc
index 747b932eefffb701959cae880b44d7c3c0ac2304..2f058715e9484c3f63f6408ba7de12dce8e50168 100644
--- a/components/pdf/renderer/pdf_accessibility_tree.cc
+++ b/components/pdf/renderer/pdf_accessibility_tree.cc
@@ -44,10 +44,7 @@ gfx::RectF ToGfxRectF(const PP_FloatRect& r) {
 PdfAccessibilityTree::PdfAccessibilityTree(
     content::RenderView* render_view)
     : render_view_(render_view),
-      render_accessibility_(nullptr),
       zoom_(1.0) {
-  content::RenderFrame* render_frame = render_view->GetMainRenderFrame();
-  render_accessibility_ = render_frame->GetRenderAccessibility();
 }
 
 PdfAccessibilityTree::~PdfAccessibilityTree() {
@@ -73,6 +70,12 @@ void PdfAccessibilityTree::SetAccessibilityPageInfo(
     const PP_PrivateAccessibilityPageInfo& page_info,
     const std::vector<PP_PrivateAccessibilityTextRunInfo>& text_runs,
     const std::vector<PP_PrivateAccessibilityCharInfo>& chars) {
+  content::RenderFrame* render_frame = render_view_->GetMainRenderFrame();

[nasko, 2016/06/28 21:59:51]

Are we guaranteed to have a main frame? We avoid making this assumption in the
face of out-of-process iframes, in which case the return value will be nullptr.
If it is guaranteed to exist, it might be useful to put a comment explaining
why.

[raymes, 2016/06/29 00:31:36]

Good question and I don't know the answer for sure. There are 2 cases where we
load the PDF plugin: 
1) If a PDF is loaded on a web page, we will load a browser plugin. This could
be at the top level (most commonly) or in an iframe. I'm not sure how browser
plugin works with OOPIF and I'm not sure how accessibility information gets
propagated for iframes with OOPIF so it would depend on those 2 things.

2) In print preview. In this case it's loaded in a same-origin subframe. In this
case we should always have access to the main frame I believe.

dmazzoni: you may want to do some tests of these cases with OOPIF to see the
result.

[dmazzoni, 2016/06/30 22:35:14]

In this case, GetMainFrame() would always work as currently implemented,
because the browser plugin always has a guest WebContents with the PDF
extension as its main frame.

It did expose another bug, though - OutOfProcessInstance wasn't loading
accessibility if it wasn't full-window. Fixed.

I added several new tests, including a PDF in an iframe and a PDF in
an OOPIF.
Ah! This case was actually wrong, thanks for pointing it out. We had
access to the main frame, yes - but that wasn't the host frame for
the PDF plug-in, so we weren't attaching the PDF's accessibility
tree to anything.

I fixed this by adding an interface to get the RenderFrame from the
instance, rather than the RenderView. Now this case works and I
added a test for Print Preview PDF accessibility too.

+  content::RenderAccessibility* render_accessibility =
+      render_frame->GetRenderAccessibility();
+  if (!render_accessibility)
+    return;
+
   uint32_t page_index = page_info.page_index;
   CHECK_GE(page_index, 0U);
   CHECK_LT(page_index, doc_info_.page_count);
@@ -171,7 +174,11 @@ void PdfAccessibilityTree::Finish() {
     update.nodes.push_back(*node);
 
   CHECK(tree_.Unserialize(update)) << update.ToString() << tree_.error();
-  render_accessibility_->SetPdfTreeSource(this);
+  content::RenderFrame* render_frame = render_view_->GetMainRenderFrame();
+  content::RenderAccessibility* render_accessibility =
+      render_frame->GetRenderAccessibility();
+  if (render_accessibility)
+    render_accessibility->SetPdfTreeSource(this);
 }
 
 void PdfAccessibilityTree::ComputeParagraphAndHeadingThresholds(
@@ -245,8 +252,12 @@ gfx::RectF PdfAccessibilityTree::ToRectF(const PP_Rect& r) {
 }
 
 ui::AXNodeData* PdfAccessibilityTree::CreateNode(ui::AXRole role) {
+  content::RenderFrame* render_frame = render_view_->GetMainRenderFrame();
+  content::RenderAccessibility* render_accessibility =
+      render_frame->GetRenderAccessibility();
+
   ui::AXNodeData* node = new ui::AXNodeData();
-  node->id = render_accessibility_->GenerateAXID();
+  node->id = render_accessibility->GenerateAXID();
   node->role = role;
   node->state = 1 << ui::AX_STATE_ENABLED | 1 << ui::AX_STATE_READ_ONLY;
   nodes_.push_back(base::WrapUnique(node));