Keep the app list start page isolated from the browser's default zoom.

chrome/browser/ui/app_list/start_page_service.cc

Index: chrome/browser/ui/app_list/start_page_service.cc
diff --git a/chrome/browser/ui/app_list/start_page_service.cc b/chrome/browser/ui/app_list/start_page_service.cc
index 9977fba3528f49650a877b49cb8f0339870f989f..027641a6de87ec62dc92eaf48900fed17f72c101 100644
--- a/chrome/browser/ui/app_list/start_page_service.cc
+++ b/chrome/browser/ui/app_list/start_page_service.cc
@@ -25,6 +25,7 @@
 #include "chrome/common/chrome_switches.h"
 #include "chrome/common/pref_names.h"
 #include "chrome/common/url_constants.h"
+#include "components/ui/zoom/zoom_controller.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/notification_details.h"
 #include "content/public/browser/notification_observer.h"
@@ -447,6 +448,21 @@ void StartPageService::Shutdown() {
   network_change_observer_.reset();
 }
 
+// Set the zoom level in DidNavigateMainFrame, as this is the earliest point
+// at which it can be done and not be affected by the ZoomController's
+// DidNavigateMainFrame handler.

[Matt Giuca, 2015/01/20 07:15:01]

Weird place for a comment (don't usually document overrides). Can you just put
it inside?

[benwells, 2015/01/20 07:31:09]

Done.

+void StartPageService::DidNavigateMainFrame(
+    const content::LoadCommittedDetails& /* details */,
+    const content::FrameNavigateParams& /* params */ ) {

[Matt Giuca, 2015/01/20 07:15:01]

Nit: No spaces in between the /* and */ (see style guide).

[benwells, 2015/01/20 07:31:09]

Done.

+  // Use a temporary zoom level for this web contents (aka isolated zoom
+  // mode) so changes to its zoom aren't reflected in any preferences.
+  ui_zoom::ZoomController::FromWebContents(contents_.get())->SetZoomMode(
+      ui_zoom::ZoomController::ZOOM_MODE_ISOLATED);
+  // Set to have a zoom level of '0', which corresponds to 100%, so the

[Matt Giuca, 2015/01/20 07:15:01]

Nit: Remove quotes around '0' (it is a number, not a char).

[benwells, 2015/01/20 07:31:09]

Done.

+  // contents aren't affected by the browser's default zoom level.
+  ui_zoom::ZoomController::FromWebContents(contents_.get())->SetZoomLevel(0);
+}
+
 void StartPageService::WebUILoaded() {
   // There's a race condition between the WebUI loading, and calling its JS
   // functions. Specifically, calling LoadContents() doesn't mean that the page
@@ -465,6 +481,12 @@ void StartPageService::LoadContents() {
   contents_delegate_.reset(new StartPageWebContentsDelegate());
   contents_->SetDelegate(contents_delegate_.get());
 
+  // The ZoomController needs to be created before the web contents is observed
+  // by this object. Otherwise it will react to DidNavigateMainFrame after this
+  // object does, resetting the zoom mode in the process.
+  ui_zoom::ZoomController::CreateForWebContents(contents_.get());
+  Observe(contents_.get());
+
   contents_->GetController().LoadURL(
       GURL(chrome::kChromeUIAppListStartPageURL),
       content::Referrer(),