Factor out skia_keep_frame_pointer. Handy with perf to get call stacks.

Today it's set when we're running a sanitizer, but it's more generally useful.  perf record -g (--call-graph) only works for me if we don't omit the frame pointer.

BUG=
R=bungeman@google.com

Author: mtklein@google.com

Review URL: https://codereview.chromium.org/41923004

git-svn-id: http://skia.googlecode.com/svn/trunk@11966 2bbb7eff-a529-9590-31e7-b0007b416f81

gyp/common_conditions.gypi

@@ -280,7 +280,6 @@
           [ 'skia_sanitizer', {
             'cflags': [
               '-fsanitize=<(skia_sanitizer)',
-              '-fno-omit-frame-pointer',
             ],
             'ldflags': [
               '-fsanitize=<(skia_sanitizer)',
@@ -304,6 +303,9 @@
               '-Wstring-conversion',
             ],
           }],
+          [ 'skia_keep_frame_pointer', {
+            'cflags': [ '-fno-omit-frame-pointer' ],
+          }],
         ],
       },
     ],

gyp/common_variables.gypi

@@ -120,8 +120,10 @@
       }],
       [ 'skia_sanitizer', {
         'skia_clang_build': 1,
+        'skia_keep_frame_pointer': 1,
       }, {
         'skia_clang_build%': 0,
+        'skia_keep_frame_pointer%': 0,
       }],
     ],