Reland Don't set -fvisibility=hidden for iOS Debug in GYP.

build/common.gypi

Index: build/common.gypi
diff --git a/build/common.gypi b/build/common.gypi
index c62e8b8dacece3f7ed7a29d6b866af58edc19cd3..b6fee19d11b19dcfb6b992ce0464803617117684 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -5074,7 +5074,6 @@
           # GCC_INLINES_ARE_PRIVATE_EXTERN maps to -fvisibility-inlines-hidden
           'GCC_INLINES_ARE_PRIVATE_EXTERN': 'YES',
           'GCC_OBJC_CALL_CXX_CDTORS': 'YES',        # -fobjc-call-cxx-cdtors
-          'GCC_SYMBOLS_PRIVATE_EXTERN': 'YES',      # -fvisibility=hidden
           'GCC_THREADSAFE_STATICS': 'NO',           # -fno-threadsafe-statics
           'GCC_TREAT_WARNINGS_AS_ERRORS': 'YES',    # -Werror
           'GCC_VERSION': '4.2',
@@ -5187,6 +5186,29 @@
               }],
             ],
           }],
+          ['OS=="mac"', {
+            'xcode_settings': {
+              'GCC_SYMBOLS_PRIVATE_EXTERN': 'YES',    # -fvisibility=hidden
+            },
+          }],
+          ['OS=="ios"', {
+            'configurations': {
+              'Debug': {
+                'xcode_settings': {
+                  # XCTests inject a dynamic library into the application. If
+                  # fvisibility is set to hidden, then some symbols needed by
+                  # XCTests are not available. Disable this setting for
+                  # Debug configuration.
+                  'GCC_SYMBOLS_PRIVATE_EXTERN': 'NO',
+                },
+              },
+              'Release': {
+                'xcode_settings': {
+                  'GCC_SYMBOLS_PRIVATE_EXTERN': 'YES',    # -fvisibility=hidden
+                },
+              },
+            },
+          }],
         ],
         'target_conditions': [
           ['_type!="static_library"', {