Add a per-host desktopScale option, available via the JS console.

remoting/webapp/crd/js/client_session.js

Index: remoting/webapp/crd/js/client_session.js
diff --git a/remoting/webapp/crd/js/client_session.js b/remoting/webapp/crd/js/client_session.js
index 4d68335fde00ad9256711aefc89df57b9ad9ce8a..0d4c32fef49b7cce900e69d00119ad14051b8957 100644
--- a/remoting/webapp/crd/js/client_session.js
+++ b/remoting/webapp/crd/js/client_session.js
@@ -129,6 +129,8 @@ remoting.ClientSession = function(signalStrategy, container, hostDisplayName,
   /** @private */
   this.resizeToClient_ = true;
   /** @private */
+  this.desktopZoom_ = 1.0;
+  /** @private */
   this.remapKeys_ = '';
   /** @private */
   this.hasReceivedFrame_ = false;
@@ -377,6 +379,7 @@ remoting.ClientSession.STATS_KEY_ROUNDTRIP_LATENCY = 'roundtripLatency';
 remoting.ClientSession.KEY_REMAP_KEYS = 'remapKeys';
 remoting.ClientSession.KEY_RESIZE_TO_CLIENT = 'resizeToClient';
 remoting.ClientSession.KEY_SHRINK_TO_FIT = 'shrinkToFit';
+remoting.ClientSession.KEY_DESKTOP_ZOOM = 'desktopZoom';
 
 /**
  * Set of capabilities for which hasCapability_() can be used to test.
@@ -502,6 +505,12 @@ remoting.ClientSession.prototype.onHostSettingsLoaded_ = function(options) {
     this.shrinkToFit_ = /** @type {boolean} */
         options[remoting.ClientSession.KEY_SHRINK_TO_FIT];
   }
+  if (remoting.ClientSession.KEY_DESKTOP_ZOOM in options &&
+      typeof(options[remoting.ClientSession.KEY_DESKTOP_ZOOM]) ==
+          'number') {
+    this.desktopZoom_ = /** @type {number} */
+        options[remoting.ClientSession.KEY_DESKTOP_ZOOM];
+  }
 
   /** @param {boolean} result */
   this.plugin_.initialize(this.onPluginInitialized_.bind(this));
@@ -772,6 +781,25 @@ remoting.ClientSession.prototype.sendPrintScreen = function() {
 }
 
 /**
+ * Sets and stores the zoom factor to apply to host sizing requests.
+ *
+ * @param {number} desktopZoom Scale factor to apply.
+ */
+remoting.ClientSession.prototype.setDesktopZoom =
+    function(desktopZoom) {
+  // Apply the new desktop zoom, if resize to client is enabled.

[Jamie, 2014/12/15 18:39:06]

Nit: resize-to-client

[Wez, 2014/12/15 21:49:42]

Done.

+  this.desktopZoom_ = desktopZoom;
+  if (this.resizeToClient_) {
+    this.notifyClientResolution_();
+  }
+
+  // Save the new desktop zoom setting.
+  var options = {};
+  options[remoting.ClientSession.KEY_DESKTOP_ZOOM] = this.desktopZoom_;
+  remoting.HostSettings.save(this.hostId_, options);
+}
+
+/**
  * Sets and stores the key remapping setting for the current host.
  *
  * @param {string} remappings Comma separated list of key remappings.
@@ -842,10 +870,7 @@ remoting.ClientSession.prototype.applyRemapKeys_ = function(apply) {
 remoting.ClientSession.prototype.setScreenMode =
     function(shrinkToFit, resizeToClient) {
   if (resizeToClient && !this.resizeToClient_) {
-    var clientArea = this.getClientArea_();
-    this.plugin_.notifyClientResolution(clientArea.width,
-                                        clientArea.height,
-                                        window.devicePixelRatio);
+    this.notifyClientResolution_();
   }
 
   // If enabling shrink, reset bump-scroll offsets.
@@ -1008,10 +1033,7 @@ remoting.ClientSession.prototype.onConnectionStatusUpdate_ =
     this.setFocusHandlers_();
     this.onDesktopSizeChanged_();
     if (this.resizeToClient_) {
-      var clientArea = this.getClientArea_();
-      this.plugin_.notifyClientResolution(clientArea.width,
-                                          clientArea.height,
-                                          window.devicePixelRatio);
+      this.notifyClientResolution_();
     }
     // Activate full-screen related UX.
     remoting.fullscreen.addListener(this.callOnFullScreenChanged_);
@@ -1104,10 +1126,7 @@ remoting.ClientSession.prototype.onSetCapabilities_ = function(capabilities) {
   this.capabilities_ = capabilities;
   if (this.hasCapability_(
       remoting.ClientSession.Capability.SEND_INITIAL_RESOLUTION)) {
-    var clientArea = this.getClientArea_();
-    this.plugin_.notifyClientResolution(clientArea.width,
-                                        clientArea.height,
-                                        window.devicePixelRatio);
+    this.notifyClientResolution_();
   }
   if (this.hasCapability_(remoting.ClientSession.Capability.GOOGLE_DRIVE)) {
     this.sendGoogleDriveAccessToken_();
@@ -1176,10 +1195,7 @@ remoting.ClientSession.prototype.onResize = function() {
     }
     var clientArea = this.getClientArea_();
     this.notifyClientResolutionTimer_ = window.setTimeout(
-        this.plugin_.notifyClientResolution.bind(this.plugin_,
-                                                 clientArea.width,
-                                                 clientArea.height,
-                                                 window.devicePixelRatio),
+        this.notifyClientResolution_.bind(this),
         kResizeRateLimitMs);
   }
 
@@ -1633,6 +1649,18 @@ remoting.ClientSession.prototype.getClientArea_ = function() {
 };
 
 /**
+ * Notifies the host of the client's current dimensions and DPI.
+ * Also takes into account per-host scaling factor, if configured.
+ * @private
+ */
+remoting.ClientSession.prototype.notifyClientResolution_ = function() {
+  var clientArea = this.getClientArea_();
+  this.plugin_.notifyClientResolution(clientArea.width * this.desktopZoom_,
+                                      clientArea.height * this.desktopZoom_,
+                                      window.devicePixelRatio);

[Jamie, 2014/12/15 18:39:06]

Don't you also need to apply the inverse scale to the plugin element? This will
only work if scale-to-fit is enabled, I think.

[Wez, 2014/12/15 21:49:42]

That's a good question.

I've added code in updateDimensions() to include the desktopScale in the
hostPixelRatio, which will mean taking it into account, up to the limit of the
devicePixelRatio, i.e. we won't down-scale smaller than 1:1 host:device pixels.

+}
+
+/**
  * @param {string} url
  * @param {number} hotspotX
  * @param {number} hotspotY