Adds scroll position/scale emulation to DevTools.

third_party/WebKit/Source/web/WebViewImpl.cpp

Index: third_party/WebKit/Source/web/WebViewImpl.cpp
diff --git a/third_party/WebKit/Source/web/WebViewImpl.cpp b/third_party/WebKit/Source/web/WebViewImpl.cpp
index 7f9d5c550cfe56d0f26f919d9bc120bda193ac41..43d06bc10e4b950906f3094a6290087892b88360 100644
--- a/third_party/WebKit/Source/web/WebViewImpl.cpp
+++ b/third_party/WebKit/Source/web/WebViewImpl.cpp
@@ -56,6 +56,7 @@
 #include "core/frame/LocalFrame.h"
 #include "core/frame/PageScaleConstraintsSet.h"
 #include "core/frame/RemoteFrame.h"
+#include "core/frame/ScrollAndScaleEmulator.h"
 #include "core/frame/Settings.h"
 #include "core/frame/SmartClip.h"
 #include "core/frame/TopControls.h"
@@ -3207,6 +3208,58 @@ WebFloatSize WebViewImpl::visualViewportSize() const
     return page()->frameHost().visualViewport().visibleRect().size();
 }
 
+void WebViewImpl::setScrollAndScaleOverride(const WebDeviceEmulationParams& params)
+{
+    if (!page() || !mainFrameImpl())
+        return;
+
+    FrameView * view = mainFrameImpl()->frameView();
+    if (!view)
+        return;
+
+    if (!m_scrollAndScaleEmulator) {
+        m_scrollAndScaleEmulator = ScrollAndScaleEmulator::create();
+
+        // Force main thread scrolling, because we do not apply scroll position
+        // overrides in the compositor thread.
+        m_scrollAndScaleEmulator->disableThreadedScrolling(page());
+    }
+
+    bool hasChanged = m_scrollAndScaleEmulator->update(
+        static_cast<IntPoint>(params.scrollPosition),
+        static_cast<FloatPoint>(params.visualViewportPosition),
+        params.visualViewportScale);
+    if (hasChanged) {
+        view->setScrollAndScaleEmulator(m_scrollAndScaleEmulator);
+        page()->frameHost().visualViewport().setScrollAndScaleEmulator(m_scrollAndScaleEmulator);
+        page()->frameHost().setUserAgentPageScaleConstraints(m_scrollAndScaleEmulator->pageScaleConstraints());
+    }
+}
+
+void WebViewImpl::clearScrollAndScaleOverride()
+{
+    if (!m_scrollAndScaleEmulator || !page() || !mainFrameImpl())
+        return;
+
+    FrameView * view = mainFrameImpl()->frameView();
+    if (!view)
+        return;
+
+    m_scrollAndScaleEmulator->restoreThreadedScrolling(page());
+
+    view->setScrollAndScaleEmulator(nullptr);
+    page()->frameHost().visualViewport().setScrollAndScaleEmulator(nullptr);
+    page()->frameHost().setUserAgentPageScaleConstraints(PageScaleConstraints());
+
+    // TODO(eseckler): For some reason, we seem to need this enforce the cleared
+    // constraints. Adding it in setScrollAndScaleOverride() makes the override
+    // ineffective, though.
+    page()->frameHost().pageScaleConstraintsSet().computeFinalConstraints();

[Eric Seckler, 2016/06/30 20:01:28]

Not sure why this line is necessary here (otherwise the cleared constraints
don't have any visible effect). Weirdly, it hurts to add it at the same place in
setScrollAndScaleOverride(), in which case the scale override doesn't have any
visible effect.

+
+    m_scrollAndScaleEmulator.clear();
+    resetScrollAndScaleState();
+}
+
 void WebViewImpl::scrollAndRescaleViewports(float scaleFactor,
     const IntPoint& mainFrameOrigin,
     const FloatPoint& visualViewportOrigin)
@@ -3340,10 +3393,22 @@ void WebViewImpl::setIgnoreViewportTagScaleLimits(bool ignore)
 
 IntSize WebViewImpl::mainFrameSize()
 {
-    // The frame size should match the viewport size at minimum scale, since the
-    // viewport must always be contained by the frame.
     FloatSize frameSize(m_size);
+
+    // The frame size should match the viewport size at minimum scale, since the
+    // viewport must always be contained by the frame. ScrollAndScaleEmulator
+    // overrides the minimum scale in the userAgentConstraints. These overrides
+    // should be ignored for this calculation.
+    if (m_scrollAndScaleEmulator) {
+        pageScaleConstraintsSet().setUserAgentConstraints(PageScaleConstraints());
+        pageScaleConstraintsSet().computeFinalConstraints();
+    }
     frameSize.scale(1 / minimumPageScaleFactor());
+    if (m_scrollAndScaleEmulator) {
+        pageScaleConstraintsSet().setUserAgentConstraints(m_scrollAndScaleEmulator->pageScaleConstraints());
+        pageScaleConstraintsSet().computeFinalConstraints();
+    }
+
     return expandedIntSize(frameSize);
 }
 
@@ -3832,10 +3897,12 @@ void WebViewImpl::setRootLayerTransform(const WebSize& rootLayerOffset, float ro
 void WebViewImpl::enableDeviceEmulation(const WebDeviceEmulationParams& params)
 {
     m_devToolsEmulator->enableDeviceEmulation(params);
+    setScrollAndScaleOverride(params);
 }
 
 void WebViewImpl::disableDeviceEmulation()
 {
+    clearScrollAndScaleOverride();
     m_devToolsEmulator->disableDeviceEmulation();
 }