Add build flag to disable hotwording.

build/common.gypi

Index: build/common.gypi
diff --git a/build/common.gypi b/build/common.gypi
index b26d0e1aaf3baa8c0bea2aa21795051e0767bb39..7a61e620ddbc48114e40de2c4e4250eae905fdcb 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -391,6 +391,9 @@
       # Web speech is enabled by default. Set to 0 to disable.
       'enable_web_speech%': 1,
 
+      # 'Ok Google' hotwording is disabled by default. Set to 1 to enable.

[Lei Zhang, 2015/06/05 03:13:46]

I think you should just check for GOOGLE_CHROME_BUILD in the code, rather than
adding this variable and #defining ENABLE_HOTWORDING. Usually, having something
like this variable and the corresponding ENABLE_HOTWORDING #define implies all
hotwording code will be build IFF this variable is set to 1.

[Anand Mistry (off Chromium), 2015/06/05 03:58:19]

Doesn't that require checking out the internal repo? I've never done it, can't
find the instructions on how to do it, and would prefer not to. But if you
insist...

+      'enable_hotwording%': 0,
+
       # Notifications are compiled in by default. Set to 0 to disable.
       'notifications%' : 1,
 
@@ -1136,6 +1139,7 @@
     'configuration_policy%': '<(configuration_policy)',
     'safe_browsing%': '<(safe_browsing)',
     'enable_web_speech%': '<(enable_web_speech)',
+    'enable_hotwording%': '<(enable_hotwording)',
     'notifications%': '<(notifications)',
     'clang_use_chrome_plugins%': '<(clang_use_chrome_plugins)',
     'mac_want_real_dsym%': '<(mac_want_real_dsym)',
@@ -2414,6 +2418,9 @@
       }, {
         'enable_hangout_services_extension%': 0,
       }],
+      ['branding=="Chrome"', {
+        'enable_hotwording%': 1,
+      }],
     ],
 
     # The path to the ANGLE library.