Disable "Ok Google" hotwording in open source builds by default.

build/common.gypi

Index: build/common.gypi
diff --git a/build/common.gypi b/build/common.gypi
index ddb075c5467320f0b4e5a1228b68ee478e3a9151..2f3f20975175f1ead0a26abc0b308fa5f7aab2c4 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -381,8 +381,10 @@
       # Web speech is enabled by default. Set to 0 to disable.
       'enable_web_speech%': 1,
 
-      # 'Ok Google' hotwording is enabled by default. Set to 0 to disable.
-      'enable_hotwording%': 1,
+      # 'Ok Google' hotwording is disabled by default in open source builds. Set
+      # to 1 to enable. (This will download a closed-source NaCl module at
+      # startup.) Chrome-branded builds have this enabled by default.
+      'enable_hotwording%': 0,
 
       # Notifications are compiled in by default. Set to 0 to disable.
       'notifications%' : 1,
@@ -813,6 +815,10 @@
           ]
         }],
 
+        ['branding=="Chrome"', {
+          'enable_hotwording%': 1,
+        }],
+
         ['OS=="android"', {
           'enable_webrtc%': 1,
         }],