Issue #80 - reinstated unified building for some large chunks of our code.

This should reduce compile complexity saving time and reducing linker stress.

dom/html/moz.build

@@ -120,7 +120,7 @@ EXPORTS.mozilla.dom += [
     'ValidityState.h',
 ]
 
-SOURCES += [
+UNIFIED_SOURCES += [
     'HTMLAllCollection.cpp',
     'HTMLAnchorElement.cpp',
     'HTMLAreaElement.cpp',
@@ -203,7 +203,6 @@ SOURCES += [
     'nsIConstraintValidation.cpp',
     'nsRadioVisitor.cpp',
     'nsTextEditorState.cpp',
-    'PluginDocument.cpp',
     'RadioNodeList.cpp',
     'TextTrackManager.cpp',
     'TimeRanges.cpp',
@@ -211,6 +210,11 @@ SOURCES += [
     'VideoDocument.cpp',
 ]
 
+SOURCES += [
+    # Includes npapi.h.
+    'PluginDocument.cpp',
+]
+
 EXTRA_COMPONENTS += [
     'htmlMenuBuilder.js',
     'htmlMenuBuilder.manifest'