Rename text track methods to make way for audio & video tracks.

- Rename various text track related methods to explicitly indicate that
  they apply to text tracks. This is to avoid confusion when audio &
  video track logic is landed.

- Renamed TextTrackList::clearOwner() to clearOwnerAndClients() and moved
  some the client clearing out of HTMLMediaElement and into TextTrackList.
  This doesn't introduce any change in behavior. It just restores some
  encapsulation.

BUG=249427
TEST=All LayoutTests still pass.

Review URL: https://codereview.chromium.org/180173002

git-svn-id: svn://svn.chromium.org/blink/trunk@167826 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Made setWholeSubtreeInvalid non-inline.

Fix for review issue in https://codereview.chromium.org/177653003/ raised
after it landed.

R=ojan
BUG=335247

Review URL: https://codereview.chromium.org/179483002

git-svn-id: svn://svn.chromium.org/blink/trunk@167827 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Refactor WebHelperPluginImpl to simplify plugin creation.

As it turns out, it's not necessary to create a Page, or even a WebFrame
at all. This was problematic for the current work to move embedder
functionality from WebViewClient to WebFrameClient since it entangled
two WebFrames with the same WebFrameClient.

A bonus side effect is the code gets a lot simpler: WebHelperPlugin will
no longer needs to be a WebWidget, and it doesn't need to carefully
construct and destruct its internal state. This allows logic specific to
WebHelperPlugin to be completely removed from WebView.

After this change rolls into Chrome, WebHelperPlugin will be completely
removed from the embedding API, as Chrome no longer needs to interact
with it at all.

BUG=346543
R=abarth@chromium.org, ddorwin@chromium.org

Review URL: https://codereview.chromium.org/175593008

git-svn-id: svn://svn.chromium.org/blink/trunk@167830 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Fix another batch of leaks in the Blink unit tests.

With this, we go from 306248 bytes leaked in 576 allocations to 21192
bytes leaked in 94 allocations.

BUG=none
R=abarth@chromium.org

Review URL: https://codereview.chromium.org/180223003

git-svn-id: svn://svn.chromium.org/blink/trunk@167831 bbb929c8-8fbe-4397-9dbb-9b2b20218538