Removes the Compiler::CompileDebugCode and Compiler::EnsureBytecode functions
and replaces them with a Compiler::Compile(Handle<SharedFunctionInfo> shared)
function. The code in compiler.cc is refactored to use this function to compile
the SharedFunctionInfo when compiling a JSFunction.

Also does some other cleanup:
 - Removes CompileUnoptimizedFunction and inlines into new Compiler function
 - Moves code to create top level SharedFunctionInfo into CompilerTopLevel and
   out of FinalizeUnoptimizedCompile.

BUG=v8:6409

Change-Id: Ic54afcd8eb005c17f3ae6b2355060846e3091ca3
Reviewed-on: https://chromium-review.googlesource.com/613760
Commit-Queue: Ross McIlroy <rmcilroy@chromium.org>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47394}