fix(composer): Pass in onFocus handler correctly to contenteditable

- Fixes issue where body lost focus when typing and focus switched to to
field
- Now passes the onFocus handler as part of a `ContenteditableExtension`

internal_packages/composer/lib/composer-view.cjsx

@@ -301,15 +301,19 @@ class ComposerView extends React.Component
     <Contenteditable
       ref={Fields.Body}
       value={@_removeQuotedText(@state.body)}
-      onFocus={ => @setState focusedField: Fields.Body}
       onChange={@_onChangeBody}
       onScrollTo={@props.onRequestScrollTo}
       onFilePaste={@_onFilePaste}
       onScrollToBottom={@_onScrollToBottom()}
-      extensions={@state.composerExtensions}
+      extensions={[@_contenteditableHandlers()].concat(@state.composerExtensions)}
       getComposerBoundingRect={@_getComposerBoundingRect}
       initialSelectionSnapshot={@_recoveredSelection} />
 
+  _contenteditableHandlers: =>
+    {
+      onFocus: => @setState(focusedField: Fields.Body)
+    }
+
   # The contenteditable decides when to request a scroll based on the
   # position of the cursor and its relative distance to this composer
   # component. We provide it our boundingClientRect so it can calculate

src/components/contenteditable/contenteditable.cjsx

@@ -42,14 +42,7 @@ class Contenteditable extends React.Component
     # Passes an absolute top coordinate to scroll to.
     onScrollTo: React.PropTypes.func
     onScrollToBottom: React.PropTypes.func
-
-    # Extension DOM Mutating handlers. See {ContenteditableExtension}
     onFilePaste: React.PropTypes.func
-    onInput: React.PropTypes.func
-    onFocus: React.PropTypes.func
-    onClick: React.PropTypes.func
-    onKeyDown: React.PropTypes.func
-    onShowContextMenu: React.PropTypes.func
 
     # A list of objects that extend {ContenteditableExtension}
     extensions: React.PropTypes.array