Windows: Support building with a custom VS toolchain (issue #1470).

git-svn-id: http://chromiumembedded.googlecode.com/svn/trunk/cef3@1950 5089003a-bbd8-11dd-ad1f-f1f9622dbc98
Fix check for WIN_CUSTOM_TOOLCHAIN (issue #1470).

git-svn-id: http://chromiumembedded.googlecode.com/svn/trunk/cef3@1952 5089003a-bbd8-11dd-ad1f-f1f9622dbc98
Windows: Use the amd64_x86 cross-compiler with custom builds (issue #1470).

git-svn-id: http://chromiumembedded.googlecode.com/svn/trunk/cef3@1954 5089003a-bbd8-11dd-ad1f-f1f9622dbc98
Update to Chromium revision 8cb76f56 (#307671)
- Linux/Mac: Load V8 initial snapshot from external bin files (see http://crbug.com/421063).
- Windows: 8.1 SDK is now required (issue #1470).
- Remove CefDOMDocument::GetSelectionStartNode and GetSelectionEndNode methods(see https://codereview.chromium.org/763043004).
- Rename internal namespace used in base headers to avoid linker conflicts with cef_sandbox.lib.

git-svn-id: http://chromiumembedded.googlecode.com/svn/trunk/cef3@1956 5089003a-bbd8-11dd-ad1f-f1f9622dbc98
Windows: Ignore C4702 unreachable code warning for binary distribution build (issue #1472).

git-svn-id: http://chromiumembedded.googlecode.com/svn/trunk/cef3@1958 5089003a-bbd8-11dd-ad1f-f1f9622dbc98