Adds an iOS implementation of gfx::Image.

ui/base/layout.cc

Index: ui/base/layout.cc
diff --git a/ui/base/layout.cc b/ui/base/layout.cc
index ffc70821eda5ad472cca9932ecc4c70d80a3848c..39c504e2368e58155e0afbafa3b9dfda1a32b5c9 100644
--- a/ui/base/layout.cc
+++ b/ui/base/layout.cc
@@ -19,7 +19,7 @@
 #include "ui/compositor/compositor.h"
 #endif  // defined(USE_AURA) && !defined(OS_WIN)
 
-#if defined(OS_MACOSX)
+#if defined(OS_MACOSX) && !defined(OS_IOS)
 #include "base/mac/mac_util.h"
 #endif
 
@@ -70,7 +70,7 @@ std::vector<ui::ScaleFactor>& GetSupportedScaleFactorsInternal() {
       new std::vector<ui::ScaleFactor>();
   if (supported_scale_factors->empty()) {
       supported_scale_factors->push_back(ui::SCALE_FACTOR_100P);
-#if defined(OS_MACOSX) && defined(ENABLE_HIDPI)
+#if defined(OS_MACOSX) && !defined(OS_IOS) && defined(ENABLE_HIDPI)

[Nico, 2012/09/14 00:52:19]

How does HiDPI code work on iOS? Seems like you'd always wanted to add 200P on
iOS?

[rohitrao (ping after 24h), 2012/09/14 01:07:18]

This bit is TBD; I still need to work out exactly which scale factors I want. 
Was planning to do this in a future CL.

(The scale factor on iOS will never change at runtime, so what I really want is
only 100P on some devices, and only 200P on others.  Will anything break if I
don't add 100P as a supported scale factor?)

[Nico, 2012/09/14 01:13:37]

SGTM. Can you add a "TODO: Figure out ios" comment?
I don't know. But it can probably made work if it doesn't.

[rohitrao (ping after 24h), 2012/09/14 01:30:29]

Added a TODO.  I'll be looking at this either tomorrow or next week, so I'll let
you know if I run into trouble.

       if (base::mac::IsOSLionOrLater())
         supported_scale_factors->push_back(ui::SCALE_FACTOR_200P);
 #elif defined(OS_WIN) && defined(ENABLE_HIDPI)