Merge to XFA: Fix all relative includes to core.

Do some IWYU to fix build errors due to files that have no #includes but
just happened to work previously because the #includes were in the right
order.

R=tsepez@chromium.org

Review URL: https://codereview.chromium.org/1407423004 .

(cherry picked from commit 9e7cd8ffb81c564e1102f6c6459ec0942a0b11ea)

Review URL: https://codereview.chromium.org/1425163004 .
diff --git a/fpdfsdk/src/javascript/JS_EventHandler.h b/fpdfsdk/src/javascript/JS_EventHandler.h
index 5b67ec4..2af19d9 100644
--- a/fpdfsdk/src/javascript/JS_EventHandler.h
+++ b/fpdfsdk/src/javascript/JS_EventHandler.h
@@ -7,8 +7,8 @@
 #ifndef FPDFSDK_SRC_JAVASCRIPT_JS_EVENTHANDLER_H_
 #define FPDFSDK_SRC_JAVASCRIPT_JS_EVENTHANDLER_H_
 
-#include "../../../core/include/fxcrt/fx_string.h"
-#include "../../../core/include/fxcrt/fx_system.h"
+#include "core/include/fxcrt/fx_string.h"
+#include "core/include/fxcrt/fx_system.h"
 
 class CJS_Context;
 class CPDFSDK_Annot;