Add a scroll offset to PDF documents to account for the top material design toolbar.

Previously the toolbar in the material design PDF UI would always cover the top
of pages when it was first loaded or when a page was navigated to using the
page selector. Now we ensure that a blank region is left at the very top of
the document when it is first loaded. This is the region that the toolbar
covers, so the document is not obscured at all. When pages are navigated to, we
ensure that the top of the selected page is always underneath the toolbar
so that it is not obscured. The one exception to this is when in fit-to-page
mode which causes the page to be zoomed to cover the entire screen, ignoring
the toolbar. This is so that users can take advantaging of filling all of the
screen real-estate with a page when that is what they want.

This is implemented by initially scrolling the document to a negative offset
(which is equal to the toolbar height). All subsequent scrolls are relative
to this initial scroll. A few small bugs that assumed there was no blank space
above the first page have also been fixed.

BUG=439114

Committed: https://crrev.com/daad0f1f879b13c8b55797ae5ce106d382283047
Cr-Commit-Position: refs/heads/master@{#341685}

Review URL: https://codereview.chromium.org/1255403002

Cr-Commit-Position: refs/heads/master@{#341861}

1 files changed, 4 insertions, 0 deletions

diff --git a/pdf/out_of_process_instance.h b/pdf/out_of_process_instance.h
index 8a3de66..1215f19 100644
--- a/pdf/out_of_process_instance.h
+++ b/pdf/out_of_process_instance.h
@@ -333,6 +333,10 @@ class OutOfProcessInstance : public pp::Instance,
   // The background color of the PDF viewer.
   uint32 background_color_;
 
+  // The blank space above the first page of the document reserved for the
+  // toolbar.
+  int top_toolbar_height_;
+
   DISALLOW_COPY_AND_ASSIGN(OutOfProcessInstance);
 };