Added gyp support for fallback data reduction proxy host

build/common.gypi

Index: build/common.gypi
diff --git a/build/common.gypi b/build/common.gypi
index 659009b71a1743958ca3f7e14fa36f1314f31aa4..a14e6072a5a8442b1847a4d30a829ca4267b6341 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -438,6 +438,7 @@
       # Platform sends memory pressure signals natively.
       'native_memory_pressure_signals%': 0,
 
+      'data_reduction_fallback_host%' : '',
       'spdy_proxy_auth_origin%' : '',
       'spdy_proxy_auth_property%' : '',
       'spdy_proxy_auth_value%' : '',
@@ -886,6 +887,7 @@
     'enable_managed_users%': '<(enable_managed_users)',
     'native_discardable_memory%': '<(native_discardable_memory)',
     'native_memory_pressure_signals%': '<(native_memory_pressure_signals)',
+    'data_reduction_fallback_host%': '<(data_reduction_fallback_host)',
     'spdy_proxy_auth_origin%': '<(spdy_proxy_auth_origin)',
     'spdy_proxy_auth_property%': '<(spdy_proxy_auth_property)',
     'spdy_proxy_auth_value%': '<(spdy_proxy_auth_value)',
@@ -2344,6 +2346,10 @@
       ['enable_managed_users==1', {
         'defines': ['ENABLE_MANAGED_USERS=1'],
       }],
+      ['data_reduction_fallback_host != ""', {
+        'defines': [
+          'DATA_REDUCTION_FALLBACK_HOST="<(data_reduction_fallback_host)"'],
+      }],
       ['spdy_proxy_auth_origin != ""', {
         'defines': ['SPDY_PROXY_AUTH_ORIGIN="<(spdy_proxy_auth_origin)"'],
       }],