Re-landing https://chromiumcodereview.appspot.com/11587012: Introduce mac_want_real_dsym GYP flag.

build/common.gypi

Index: build/common.gypi
===================================================================
--- build/common.gypi	(revision 173892)
+++ build/common.gypi	(working copy)
@@ -252,6 +252,10 @@
       # Notifications are compiled in by default. Set to 0 to disable.
       'notifications%' : 1,
 
+      # Use dsymutil to generate real .dSYM files on Mac. The default is 0 for
+      # regular builds and 1 for ASan builds.
+      'mac_want_real_dsym%': 'default',
+
       # If this is set, the clang plugins used on the buildbot will be used.
       # Run tools/clang/scripts/update.sh to make sure they are compiled.
       # This causes 'clang_chrome_plugins_flags' to be set.
@@ -677,6 +681,7 @@
     'input_speech%': '<(input_speech)',
     'notifications%': '<(notifications)',
     'clang_use_chrome_plugins%': '<(clang_use_chrome_plugins)',
+    'mac_want_real_dsym%': '<(mac_want_real_dsym)',
     'asan%': '<(asan)',
     'tsan%': '<(tsan)',
     'tsan_blacklist%': '<(tsan_blacklist)',
@@ -3362,9 +3367,27 @@
           # variables that are intended to be set to different values in
           # different targets, like these.
           'mac_pie': 1,        # Most executables can be position-independent.
-          'mac_real_dsym': 0,  # Fake .dSYMs are fine in most cases.
           # Strip debugging symbols from the target.
           'mac_strip': '<(mac_strip_release)',
+          'conditions': [
+            ['asan==1', {
+              'conditions': [
+                ['mac_want_real_dsym=="default"', {
+                  'mac_real_dsym': 1,
+                }, {
+                  'mac_real_dsym': '<(mac_want_real_dsym)'
+                }],
+              ],
+            }, {
+              'conditions': [
+                ['mac_want_real_dsym=="default"', {
+                  'mac_real_dsym': 0, # Fake .dSYMs are fine in most cases.
+                }, {
+                  'mac_real_dsym': '<(mac_want_real_dsym)'
+                }],
+              ],
+            }],
+          ],
         },
         'xcode_settings': {
           'GCC_DYNAMIC_NO_PIC': 'NO',               # No -mdynamic-no-pic