Add flag to experiments to force high DPI mode.

chrome/app/generated_resources.grd

Index: chrome/app/generated_resources.grd
diff --git a/chrome/app/generated_resources.grd b/chrome/app/generated_resources.grd
index 78c43e73daa246f62647aa88a3d5ce982d6a561b..166a1b1c81b04e3a7bc645d490b2f8481fd6f3e0 100644
--- a/chrome/app/generated_resources.grd
+++ b/chrome/app/generated_resources.grd
@@ -5132,6 +5132,12 @@ Keep your key file in a safe place. You will need it to create new versions of y
       <message name="IDS_FLAGS_FORCE_COMPOSITING_MODE_DESCRIPTION" desc="Description of the 'Force compositing mode' lab.">
         Uses GPU accelerated compositing on all pages, not just those that include GPU-accelerated layers.
       </message>
+      <message name="IDS_FLAGS_FORCE_HIGH_DPI_NAME" desc="Name of the 'Force high DPI mode' lab.">
+        Force high DPI mode
+      </message>
+      <message name="IDS_FLAGS_FORCE_HIGH_DPI_DESCRIPTION" desc="Description of the 'Force high DPI mode' lab.">
+        Overrides the device display density to force the use of high DPI mode and assets.
+      </message>
       <message name="IDS_FLAGS_IGNORE_GPU_BLACKLIST_NAME" desc="Name of the 'Ignore GPU blacklist' lab.">
         Override software rendering list
       </message>