Mac: Fix renderer idle cpu usage regression.

chrome/browser/tab_contents/tab_contents_view_mac.mm

Index: chrome/browser/tab_contents/tab_contents_view_mac.mm
diff --git a/chrome/browser/tab_contents/tab_contents_view_mac.mm b/chrome/browser/tab_contents/tab_contents_view_mac.mm
index 92cbe2d4504552a7d171f12d7ff320dc5420f494..9de79b94291eda325361372044f6bc6ee717d853 100644
--- a/chrome/browser/tab_contents/tab_contents_view_mac.mm
+++ b/chrome/browser/tab_contents/tab_contents_view_mac.mm
@@ -154,10 +154,10 @@ void TabContentsViewMac::StartDragging(
 }
 
 void TabContentsViewMac::RenderViewCreated(RenderViewHost* host) {
-  // We want updates whenever the intrinsic width of the webpage
-  // changes. Put the RenderView into that mode.
-  int routing_id = host->routing_id();
-  host->Send(new ViewMsg_EnablePreferredSizeChangedMode(routing_id));
+  // We want updates whenever the intrinsic width of the webpage changes.
+  // Put the RenderView into that mode. The preferred width is used for example
+  // when the "zoom" button in the browser window is clicked.
+  host->EnablePreferredSizeChangedMode(kPreferredSizeWidth);
 }
 
 void TabContentsViewMac::SetPageTitle(const std::wstring& title) {