Enable multithreaded GPU compositing of web content by default.

Enable multithreaded GPU compositing of web content by default, this also enables pinch gesture support on Tizen.
Merge pull request #933 from pozdnyakov/EnableThreadedCompositing

Enable multithreaded GPU compositing of web content by default.
[Extensions] Remove unused function
Merge pull request #934 from cmarcelo/remove-dead-code

[Extensions] Remove unused function
[Extensions] Use a vector instead of a map for extension modules

In XWalkModuleSystem, use a vector instead of a map for extension
modules. The number of modules is small and we'll benefit from being
able to easily get sorted iteration later to identify the extension
modules that can be loaded on demand.
Merge pull request #910 from jeez/refactor-register-extension

[Extensions] Refactoring XWalkExtensionService::RegisterExtension
Merge pull request #937 from cmarcelo/extension-modules-vector

[Extensions] Use a vector instead of a map for extension modules
[Extensions] Remove old comment From XWalkExtensionProcessHost.
[Extensions] Use OnRenderProcessHostCreated to create a ExtensionProcessHost

This patch postpones the creation of a XWalkExtensionProcessHost until
a new RenderProcessHost is created. For achieving that we also had to
delay calling XWalkExtensionProcessHost::RegisterExternalExtensions.
[Extensions] Create one ExtensionProcess per RenderProcess
[Extensions] Add a InProcess ExtensionServer per RenderProcess
[Extensions] Add an InProcess MessageFilter per RenderProcess
[Extensions] Refactor XWalkExtensionService::OnRenderProcessHostCreated

Added two helper functions to XWalkExtensionService:
CreateExtensionProcessHost() and CreateInProcessExtensionServer().
[Extensions] Add test for 1-EP-per-RP