Add gyp define for optimization level

gyp/common_conditions.gypi

Index: gyp/common_conditions.gypi
===================================================================
--- gyp/common_conditions.gypi	(revision 9698)
+++ gyp/common_conditions.gypi	(working copy)
@@ -76,7 +76,7 @@
             'msvs_settings': {
               'VCCLCompilerTool': {
                 'DebugInformationFormat': '3',      # programDatabase (/Zi)
-                'Optimization': '3',                # full (/Ox)
+                'Optimization': '<(skia_release_optimization_level)', # full (/Ox)

[epoger, 2013/06/20 18:25:55]

please delete the comment, which pertains to the value '3' specifically

More importantly, do we have any guarantee that the MSVS and GCC optimization
levels will move in concert?  (I think it may just be a happy accident that they
are both set to '3' right now...)

[bungeman-skia, 2013/06/20 19:19:35]

gcc uses 0 (none), 1 (basic, local), 2 (everything that's spec compliant and
doesn't make code bigger), 3 (stuff that might make the code bigger / slower)

clang is like gcc, but adds 4 (use ltcg)

the values for msvs are 0 (none), 1 (size), 2 (speed), 3 (full).

Is the idea to have a flag which compiles without optimization? That would be an
easier conditional.

                 'WholeProgramOptimization': 'true', #/GL
                # Changing the floating point model requires rebaseling gm images
                #'FloatingPointModel': '2',          # fast (/fp:fast)
@@ -137,7 +137,10 @@
             'cflags': ['-g']
           },
           'Release': {
-            'cflags': ['-O3 -g'],

[bungeman-skia, 2013/06/20 19:19:35]

Huh, I thought the last time we mucked with this we set this to 2. In modern gcc
-O2 is often faster that -O3 just because the code size is smaller. I have no
idea if we've actually tested on Skia though.

+            'cflags': [
+              '-O<(skia_release_optimization_level)',
+              '-g'
+            ],
             'defines': [ 'NDEBUG' ],
           },
         },
@@ -235,7 +238,7 @@
           },
           'Release': {
             'xcode_settings': {
-              'GCC_OPTIMIZATION_LEVEL': '3',
+              'GCC_OPTIMIZATION_LEVEL': '<(skia_release_optimization_level)',
             },
             'defines': [ 'NDEBUG' ],
           },
@@ -301,7 +304,7 @@
           },
           'Release': {
             'xcode_settings': {
-              'GCC_OPTIMIZATION_LEVEL': '3',
+              'GCC_OPTIMIZATION_LEVEL': '<(skia_release_optimization_level)',
             },
             'defines': [ 'NDEBUG' ],
           },