Improve <webview> autosize:

content/renderer/browser_plugin/browser_plugin.cc

Index: content/renderer/browser_plugin/browser_plugin.cc
diff --git a/content/renderer/browser_plugin/browser_plugin.cc b/content/renderer/browser_plugin/browser_plugin.cc
index 23537a542313561bfda7288586037934c11fa211..46181fc7cf39d1d63392be13bed61a3c47a00b5a 100644
--- a/content/renderer/browser_plugin/browser_plugin.cc
+++ b/content/renderer/browser_plugin/browser_plugin.cc
@@ -321,6 +321,7 @@ void BrowserPlugin::UpdateGuestAutoSizeState(bool current_auto_size) {
   if (current_auto_size) {
     GetDamageBufferWithSizeParams(&auto_size_params, &resize_guest_params);
   } else {
+    last_seen_auto_view_size_ = gfx::Size();
     GetDamageBufferWithSizeParams(NULL, &resize_guest_params);
   }
   resize_ack_received_ = false;
@@ -508,7 +509,21 @@ void BrowserPlugin::OnUpdateRect(
 
   auto_size_ack_pending_ = false;
 
-  if ((!auto_size && (width() != params.view_size.width() ||
+  bool needs_new_damage_buffer = false;
+  if (auto_size && !params.view_size.IsEmpty()) {
+    if (params.view_size.width() > last_seen_auto_view_size_.width() ||
+        params.view_size.height() > last_seen_auto_view_size_.height()) {
+      // The width or height of the view size increased, so we would need new
+      // damage buffer to hold increased pixels.
+      needs_new_damage_buffer = true;

[Fady Samuel, 2013/08/27 14:16:18]

I don't understand this fix. We set the damage buffer equal to the maximum
constraints, right? When would this happen?

[lazyboy, 2013/08/27 23:22:17]

As discussed offline, the CL changed quite a bit and we are detecting this case
via dirty flag now.

+      // A repaint is necessary to receive a UpdateRect for new size.
+      resize_guest_params.repaint = true;
+    }
+    last_seen_auto_view_size_ = params.view_size;
+  }
+
+  if (needs_new_damage_buffer ||
+      (!auto_size && (width() != params.view_size.width() ||
                       height() != params.view_size.height())) ||
       (auto_size && (!InAutoSizeBounds(params.view_size))) ||
       GetDeviceScaleFactor() != params.scale_factor) {