Clean up RenderEmbeddedObject.h.

* Consolidate the redundant protected and private sections.
* Remove RenderEmbeddedObject::paintSnapshotImage, which is never defined or
  called.
* Move RenderEmbeddedObject::paintContents next to the other painting methods.
* Remove RenderEmbeddedObject.h include from ChromeClient.h (which does not use
  it) and handle resulting build errors by filling in includes at sites which
  previously got them via ChromeClient.h -> RenderEmbeddedObject.h.

Review URL: https://codereview.chromium.org/364233003

git-svn-id: svn://svn.chromium.org/blink/trunk@177491 bbb929c8-8fbe-4397-9dbb-9b2b20218538