Revert "Forward declaration for Isolate / Platform in libplatform.h." and "Fixes d8 on windows following.".

This reverts commit 0f57ce8f.
and 3245b8cb for breaking Chromium
compile.

TBR=machenbach@chromium.org

Review URL: https://codereview.chromium.org/743533003

Cr-Commit-Position: refs/heads/master@{#25411}

Reduces dependencies on #include files, making it easier for other
build systems to include this library.

BUG=

Review URL: https://codereview.chromium.org/740493002

Cr-Commit-Position: refs/heads/master@{#25408}

BUG=none
LOG=n
R=marja@chromium.org

Review URL: https://codereview.chromium.org/363303002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22187 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

TBR=yangguo@chromium.org
LOG=n
BUG=none

Review URL: https://codereview.chromium.org/367293002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22181 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

Also remove the "use default platform" compile flag. Instead, the embedder
has to provide the platform.

Change all binaries to use the default platfrom from libplatform.

Unless --job-based-sweeping is passed, nothing uses the platform yet, so
nothing will break for embedders (yet).

BUG=none
R=jkummerow@chromium.org
LOG=y

Review URL: https://codereview.chromium.org/345903004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22180 ce2b1a6d-e550-0410-aec6-3dcde31c8c00