fast/filesystem/workers/file-writer-write-overlapped.html crashes on release try bots.

BUG=86340
TBR=dominicc@chromium.org

Review URL: https://codereview.chromium.org/23171016

git-svn-id: svn://svn.chromium.org/blink/trunk@156278 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Refactoring: Rename isMediaElement to isHTMLMediaElement, toMediaElement to toHTMLMediaElement for consistency, and use toHTMLMediaElement isntead of static_cast.

Type check functions should be named as isClassName, and cast functions should
be named as toClassName.

BUG=

Review URL: https://chromiumcodereview.appspot.com/23122004

git-svn-id: svn://svn.chromium.org/blink/trunk@156279 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Refactoring: Page::editorClient and Editor::client should return references.

Page::editorClient is never null.
Editor::client can't access a Page in some cases, and we use
EmptyEditorClient in such cases.

BUG=
TEST=none; This should not make behavior changes.

Review URL: https://chromiumcodereview.appspot.com/23112008

git-svn-id: svn://svn.chromium.org/blink/trunk@156280 bbb929c8-8fbe-4397-9dbb-9b2b20218538