Issue #26 Part 2a: make more EME code conditional.

- Exclude missed MediaKey functions and CDMProxy code.
- Exclude EME APIs frm being built (webidl change)
- Fix tests in --disable-eme state

dom/media/gtest/moz.build

@@ -28,6 +28,11 @@ UNIFIED_SOURCES += [
     'TestWebMBuffered.cpp',
 ]
 
+if CONFIG['MOZ_EME']:
+    UNIFIED_SOURCES += [
+        'TestEME.cpp',
+    ]
+
 if CONFIG['MOZ_WEBM_ENCODER']:
     UNIFIED_SOURCES += [
         'TestVideoTrackEncoder.cpp',