Adds DevTools commands for forced viewport override.

third_party/WebKit/Source/core/frame/FrameView.h

Index: third_party/WebKit/Source/core/frame/FrameView.h
diff --git a/third_party/WebKit/Source/core/frame/FrameView.h b/third_party/WebKit/Source/core/frame/FrameView.h
index 8c49dc36344679d0e98243295936aad2357daca9..5ee16845049854a1d7b49acc6268d266e3aadf8f 100644
--- a/third_party/WebKit/Source/core/frame/FrameView.h
+++ b/third_party/WebKit/Source/core/frame/FrameView.h
@@ -191,6 +191,7 @@ public:
     void setInputEventsTransformForEmulation(const IntSize&, float);
 
     void setScrollPosition(const DoublePoint&, ScrollType, ScrollBehavior = ScrollBehaviorInstant) override;
+    void didChangeScrollOffset();
 
     void didUpdateElasticOverscroll();
 
@@ -450,6 +451,11 @@ public:
     IntRect visibleContentRect(IncludeScrollbarsInRect = ExcludeScrollbars) const override;
     IntSize visibleContentSize(IncludeScrollbarsInRect = ExcludeScrollbars) const;
 
+    // Clips the provided rect to the visible content area. For this purpose, we
+    // also query the chrome client for any active overrides to the visible area
+    // (e.g. DevTool's viewport override).
+    void clipPaintRect(FloatRect*) const;

[chrishtr, 2016/08/22 22:00:42]

Why provide a clipPaintRect method instead of just returning the rect to clip
by?

[Eric Seckler, 2016/08/23 09:32:18]

Actually, because I was thinking we could move the mainFrameClipsContent() check
from CompositedLayerMapping there (and simply not clip if it is false) for the
time being. See also the comment below about eventually unifying
record_whole_document with clipping to the device viewport.

On 2016/08/22 22:22:06, dgozman wrote:
I agree, that would be optimal - provided that we are correct in the assumption
that Android WebView sets the device viewport size to the size of the canvas
provided to WebView.onDraw(). In any case, I think changing the behavior of
record_whole_document will require some further discussion with Android WebView
folks, since it may require changes in public WebView API
(record_whole_document/enableSlowWholeDocumentDraw() should probably be renamed
/ comments updated). If possible, I'd prefer not to make this patch dependent on
the outcome of that discussion, so would suggest to tackle this as a follow-up.
Does that sound reasonable?

+
     // Functions for getting/setting the size of the document contained inside the FrameView (as an IntSize or as individual width and height
     // values).
     IntSize contentsSize() const override; // Always at least as big as the visibleWidth()/visibleHeight().
@@ -878,6 +884,7 @@ private:
     DoubleSize m_pendingScrollDelta;
     DoublePoint m_scrollPosition;
     IntSize m_contentsSize;
+    WTF::Optional<IntRect> m_visibleContentRectForPainting;
 
     int m_scrollbarsAvoidingResizer;
     bool m_scrollbarsSuppressed;