Adds DevTools commands for forced viewport override.

third_party/WebKit/Source/web/ChromeClientImpl.h

Index: third_party/WebKit/Source/web/ChromeClientImpl.h
diff --git a/third_party/WebKit/Source/web/ChromeClientImpl.h b/third_party/WebKit/Source/web/ChromeClientImpl.h
index 7c949a168ada410cf93fb614e9599c551890cac9..cbf8f15a823ae8215958a23d0c21b2553d7fce8f 100644
--- a/third_party/WebKit/Source/web/ChromeClientImpl.h
+++ b/third_party/WebKit/Source/web/ChromeClientImpl.h
@@ -104,9 +104,11 @@ public:
     IntRect viewportToScreen(const IntRect&, const Widget*) const override;
     float windowToViewportScalar(const float) const override;
     WebScreenInfo screenInfo() const override;
+    WTF::Optional<IntRect> visibleContentRectForPainting() const override;
     void contentsSizeChanged(LocalFrame*, const IntSize&) const override;
     void pageScaleFactorChanged() const override;
     float clampPageScaleFactorToLimits(float scale) const override;
+    void mainFrameScrollOffsetChanged() const override;
     void layoutUpdated(LocalFrame*) const override;
     void showMouseOverURL(const HitTestResult&) override;
     void setToolTip(const String& tooltipText, TextDirection) override;