Disable periodic serialization for buffers > 2MB

Writing so much data to IndexedDB is blocking the main thread for
perceptible amounts of time. A patch-based representation of the
modified state could allows us to pay only for what has changed, but is
too complex to justify implementing right now to support full crash
recovery for large files.

Signed-off-by: Max Brunsfeld <maxbrunsfeld@github.com>

src/project.coffee

@@ -70,7 +70,15 @@ class Project extends Model
   serialize: (options={}) ->
     deserializer: 'Project'
     paths: @getPaths()
-    buffers: _.compact(@buffers.map (buffer) -> buffer.serialize({markerLayers: options.isUnloading is true}) if buffer.isRetained())
+    buffers: _.compact(@buffers.map (buffer) ->
+      if buffer.isRetained()
+        state = buffer.serialize({markerLayers: options.isUnloading is true})
+        # Skip saving large buffer text unless unloading to avoid blocking main thread
+        if not options.isUnloading and state.text.length > 2 * 1024 * 1024
+          delete state.text
+          delete state.digestWhenLastPersisted
+        state
+    )
 
   ###
   Section: Event Subscription