Adds scroll position/scale emulation to DevTools.

third_party/WebKit/Source/web/DevToolsEmulator.cpp

Index: third_party/WebKit/Source/web/DevToolsEmulator.cpp
diff --git a/third_party/WebKit/Source/web/DevToolsEmulator.cpp b/third_party/WebKit/Source/web/DevToolsEmulator.cpp
index 848f4e121489e3eb3daee48891475e134128abbc..dc6c2c52362b2daca1d0df7c46ec4c6b57c09870 100644
--- a/third_party/WebKit/Source/web/DevToolsEmulator.cpp
+++ b/third_party/WebKit/Source/web/DevToolsEmulator.cpp
@@ -239,7 +239,6 @@ void DevToolsEmulator::disableDeviceEmulation()
     disableMobileEmulation();
     m_webViewImpl->setCompositorDeviceScaleFactorOverride(0.f);
     m_webViewImpl->setRootLayerTransform(WebSize(0.f, 0.f), 1.f);
-    m_webViewImpl->setPageScaleFactor(1.f);
     // mainFrameImpl() could be null during cleanup or remote <-> local swap.
     if (m_webViewImpl->mainFrameImpl()) {
         if (Document* document = m_webViewImpl->mainFrameImpl()->frame()->document())
@@ -314,6 +313,7 @@ void DevToolsEmulator::disableMobileEmulation()
     m_webViewImpl->setDefaultPageScaleLimits(
         m_originalDefaultMinimumPageScaleFactor,
         m_originalDefaultMaximumPageScaleFactor);
+    m_webViewImpl->page()->frameHost().visualViewport().setScale(1.f);

[bokan, 2016/07/04 22:44:09]

I think this does actually belong in disableDeviceEmulation. We need this on
desktop emulation since it can include a touch screen which means the user can
zoom in themselves. We still want to reset the page scale in that case.

You may want to try calling setNeedsReset(true) instead and moving the layout
call below into disableDeviceEmulation as well. That way we'll reset the page
scale to the minimum after the layout.

[Eric Seckler, 2016/07/05 16:46:51]

Done.

     // mainFrameImpl() could be null during cleanup or remote <-> local swap.
     if (m_webViewImpl->mainFrameImpl())
         m_webViewImpl->mainFrameImpl()->frameView()->layout();