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..9e0b170d82c0e4d5a6c01afed5ea7399df8b0a99 100644
--- a/third_party/WebKit/Source/web/DevToolsEmulator.cpp
+++ b/third_party/WebKit/Source/web/DevToolsEmulator.cpp
@@ -239,9 +239,10 @@ void DevToolsEmulator::disableDeviceEmulation()
     disableMobileEmulation();
     m_webViewImpl->setCompositorDeviceScaleFactorOverride(0.f);
     m_webViewImpl->setRootLayerTransform(WebSize(0.f, 0.f), 1.f);
-    m_webViewImpl->setPageScaleFactor(1.f);
+    m_webViewImpl->resetScaleStateImmediately();
     // mainFrameImpl() could be null during cleanup or remote <-> local swap.
     if (m_webViewImpl->mainFrameImpl()) {
+        m_webViewImpl->mainFrameImpl()->frameView()->layout();
         if (Document* document = m_webViewImpl->mainFrameImpl()->frame()->document())
             document->mediaQueryAffectingValueChanged();
     }
@@ -314,9 +315,6 @@ void DevToolsEmulator::disableMobileEmulation()
     m_webViewImpl->setDefaultPageScaleLimits(
         m_originalDefaultMinimumPageScaleFactor,
         m_originalDefaultMaximumPageScaleFactor);
-    // mainFrameImpl() could be null during cleanup or remote <-> local swap.
-    if (m_webViewImpl->mainFrameImpl())
-        m_webViewImpl->mainFrameImpl()->frameView()->layout();

[dgozman, 2016/07/21 20:54:08]

This is still needed when we toggle between mobile/desktop emulation (called
from enableDeviceEmulation).

[Eric Seckler, 2016/07/22 14:44:48]

Right, thanks. I think it still makes sense to reset the scale through
resetScaleStateImmediately() in disableDeviceMetrics, which needs a layout. I
think a reasonable solution is to remove the layout() from
enableMobileEmulation, too, and add it to enableDeviceEmulation instead. Done.

 }
 
 void DevToolsEmulator::setTouchEventEmulationEnabled(bool enabled)