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

public/web/WebDevToolsAgentClient.h

Index: public/web/WebDevToolsAgentClient.h
diff --git a/public/web/WebDevToolsAgentClient.h b/public/web/WebDevToolsAgentClient.h
index f8538735e5248ebfe6ddcbfc7829fc088fd19784..5b9b516ca3cb3eb2ae67e18194f220be008dc4a1 100644
--- a/public/web/WebDevToolsAgentClient.h
+++ b/public/web/WebDevToolsAgentClient.h
@@ -37,6 +37,8 @@
 namespace WebKit {
 class WebString;
 struct WebDevToolsMessageData;
+struct WebRect;
+struct WebSize;
 
 class WebDevToolsAgentClient {
 public:
@@ -83,6 +85,15 @@ public:
 
     virtual void setTraceEventCallback(TraceEventCallback) { }
 
+    // Called to emulate device dimensions, scale factor and input. Window should
+    // occupy the whole device screen, while the view should be located at |viewRect|.
+    // With |fitToView| set, contents should be scaled down to fit into embedder window.
+    // All sizes are measured in device independent pixels.
+    virtual void enableDeviceEmulation(
+        const WebSize& screenSize, const WebRect& viewRect,
+        float deviceScaleFactor, bool fitToView) { }
+    virtual void disableDeviceEmulation() { }
+
 protected:
     ~WebDevToolsAgentClient() { }
 };