Conditionally build support for Pepper-based CDMs.

Adds enable_pepper_cdms and ENABLE_PEPPER_CDMS to control building of this logic.
Previously, it was built for all platforms, but not all platforms use Pepper.

TEST=content_browsertests on platforms with and without Pepper CDM support

Review URL: https://chromiumcodereview.appspot.com/15028015

git-svn-id: http://src.chromium.org/svn/trunk/src/build@201738 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

common.gypi

@@ -1412,6 +1412,12 @@
         'use_cups%': 0,
       }],
 
+      ['enable_plugins==1 and (OS=="linux" or OS=="mac" or OS=="win" or google_tv==1)', {
+        'enable_pepper_cdms%': 1,
+      }, {
+        'enable_pepper_cdms%': 0,
+      }],
+
       # Native Client glibc toolchain is enabled
       # by default except on arm and mips.
       ['target_arch=="arm" or target_arch=="mipsel"', {
@@ -1912,6 +1918,9 @@
       ['enable_viewport==1', {
         'defines': ['ENABLE_VIEWPORT'],
       }],
+      ['enable_pepper_cdms==1', {
+        'defines': ['ENABLE_PEPPER_CDMS'],
+      }],
       ['configuration_policy==1', {
         'defines': ['ENABLE_CONFIGURATION_POLICY'],
       }],