[DevTools] Blink-side APIs for device metrics emulation in content.

public/web/WebView.h

Index: public/web/WebView.h
diff --git a/public/web/WebView.h b/public/web/WebView.h
index a9457988aaf0eed8f7a9bc4d541cd11eb5b01525..f9c50f5d0100de04ce29c9ebe4a92a59ba55e6dd 100644
--- a/public/web/WebView.h
+++ b/public/web/WebView.h
@@ -401,6 +401,15 @@ public:
     virtual void setInspectorSetting(const WebString& key,
                                      const WebString& value) = 0;
 
+    // Set an override of device scale factor passed from WebView to
+    // compositor. Pass zero to cancel override. This is used to implement
+    // device metrics emulation.
+    virtual void setCompositorDeviceScaleFactorOverride(float) = 0;
+
+    // Set scaling transformation on the root composited layer. This is used
+    // to implement device metrics emulation.
+    virtual void setRootLayerScaleTransform(float) = 0;
+
     // The embedder may optionally engage a WebDevToolsAgent.  This may only
     // be set once per WebView.
     virtual WebDevToolsAgent* devToolsAgent() = 0;