Add a gyp flag to allow removing dependency on ppapi.

build/common.gypi

Index: build/common.gypi
diff --git a/build/common.gypi b/build/common.gypi
index c94af17e0566d3d4507471328f26557b629fd948..5c9920dae3028d4ccc22825daeed014211372927 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -376,6 +376,9 @@
       # Enable plug-in installation by default.
       'enable_plugin_installation%': 1,
 
+      # Enable ppapi by default.
+      'enable_ppapi%': 1,
+
       # Enable protector service by default.
       'enable_protector_service%': 1,
 
@@ -525,6 +528,12 @@
         }],
 
         ['OS=="android" or OS=="ios"', {
+          'enable_ppapi%': 0,
+        }, {
+          'enable_ppapi%': 1,
+        }],
+
+        ['OS=="android" or OS=="ios"', {
           'enable_protector_service%': 0,
         }, {
           'enable_protector_service%': 1,
@@ -674,6 +683,7 @@
     'enable_web_intents%': '<(enable_web_intents)',
     'enable_web_intents_tag%': '<(enable_web_intents_tag)',
     'enable_plugin_installation%': '<(enable_plugin_installation)',
+    'enable_ppapi%': '<(enable_ppapi)',
     'enable_protector_service%': '<(enable_protector_service)',
     'enable_session_service%': '<(enable_session_service)',
     'enable_themes%': '<(enable_themes)',
@@ -1869,6 +1879,9 @@
       ['enable_plugin_installation==1', {
         'defines': ['ENABLE_PLUGIN_INSTALLATION=1'],
       }],
+      ['enable_ppapi==1', {
+        'defines': ['ENABLE_PPAPI=1'],
+      }],
       ['enable_protector_service==1', {
         'defines': ['ENABLE_PROTECTOR_SERVICE=1'],
       }],