Original patch by rlarocque@chromium.org at http://codereview.chromium.org/7633077/

Original patch by rlarocque@chromium.org at http://codereview.chromium.org/7633077/

Fragment syncapi.h into sync/internal_api/* 

This commit splits syncapi.cc and syncapi.h into many files. Most of these files have been moved to the newly created chrome/browser/sync/internal_api. 

Each of the following classes now have their own .cc and .h files: 
- BaseNode 
- ReadNode 
- WriteNode 
- BaseTransaction 
- ReadTransaction 
- WriteTransaction 
- UserShare 
- SyncManager 

Functions formerly declared at file-scope in syncapi.cc and shared among several classes are now declared in engine/syncapi_internal.h. We intend to use DEPS rules to prevent these functions from being included in non-syncapi classes. 

Test classes closely related to syncapi.h classes have been moved from engine to internal_api. 

This change necessarily touches the #include lists for lots of files and some of the sources lists in .gyp. 

This change should have no effect on program behaviour. 

BUG=19878
TEST=

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=97238