Revert 289403 "Update iOS deployment target to 7.0"

This appears to have broken gfx_unittests on iOS:

http://build.chromium.org/p/chromium.mac/builders/iOS%20Simulator%20%28dbg%29/builds/17689

> Update iOS deployment target to 7.0
> 
> iOS 6 will no longer be supported.
> 
> Replaces deprecated sizeWithFont: with sizeWithAttributes: (adding a
> ceilf since according to the internet, the former rounds up, and the
> latter does not) to fix compilation.
> 
> BUG=402921
> 
> Review URL: https://codereview.chromium.org/463333002

TBR=stuartmorgan@chromium.org

Review URL: https://codereview.chromium.org/473883002

Cr-Commit-Position: refs/heads/master@{#289510}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@289510 0039d316-1c4b-4281-b951-d872f2087c98

build/common.gypi

@@ -1618,7 +1618,7 @@
         # not using the "current" SDK.
         'ios_sdk%': '',
         'ios_sdk_path%': '',
-        'ios_deployment_target%': '7.0',
+        'ios_deployment_target%': '6.0',
 
         'conditions': [
           # ios_product_name is set to the name of the .app bundle as it should
@@ -5020,10 +5020,6 @@
                   'CLANG_CXX_LIBRARY': 'libc++',  # -stdlib=libc++
                 }]
               ],
-            }, {
-              # The default for deployment target of 7.0+ is libc++, so force
-              # the old behavior unless libc++ is enabled.
-              'CLANG_CXX_LIBRARY': 'libstdc++',  # -stdlib=libstdc++
             }],
           ],
         },

ui/gfx/platform_font_ios.mm

@@ -6,8 +6,6 @@
 
 #import <UIKit/UIKit.h>
 
-#include <cmath>
-
 #include "base/basictypes.h"
 #include "base/strings/sys_string_conversions.h"
 #include "base/strings/utf_string_conversions.h"
@@ -112,8 +110,7 @@ void PlatformFontIOS::CalculateMetrics() {
   height_ = font.lineHeight;
   ascent_ = font.ascender;
   cap_height_ = font.capHeight;
-  NSDictionary* attributes = @{ NSFontAttributeName : font };
-  average_width_ = std::ceil([@"x" sizeWithAttributes:attributes].width);
+  average_width_ = [@"x" sizeWithFont:font].width;
 }
 
 ////////////////////////////////////////////////////////////////////////////////

ui/gfx/text_utils_ios.mm

@@ -20,8 +20,7 @@ int GetStringWidth(const base::string16& text, const FontList& font_list) {
 float GetStringWidthF(const base::string16& text, const FontList& font_list) {
   NSString* ns_text = base::SysUTF16ToNSString(text);
   NativeFont native_font = font_list.GetPrimaryFont().GetNativeFont();
-  NSDictionary* attributes = @{ NSFontAttributeName : native_font };
-  return std::ceil([ns_text sizeWithAttributes:attributes].width);
+  return [ns_text sizeWithFont:native_font].width;
 }
 
 }  // namespace gfx