Include headers, not cc files, to fix duplicate symbols

Some builds failed with duplicate symbols because
code was compiled twice. Most builds were ok because of the
linker optimization to ignore object files that are
completely unused. In jumbo builds there were no object
files that were completely unused so the linker complained
loudly.

Also, since some code is used outside the accessibility
component, in unittests, that code needs to be exported.

TBR=almaher@microsoft.com,dmazzoni@chromium.org

Bug: 928948
Change-Id: I77aeb8beff451be16b0d5f8fe4d62e70f7c66eae
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1549127
Reviewed-by: Daniel Bratell <bratell@opera.com>
Commit-Queue: Daniel Bratell <bratell@opera.com>
Cr-Commit-Position: refs/heads/master@{#647198}
diff --git a/ui/accessibility/platform/ax_platform_node_textchildprovider_win.h b/ui/accessibility/platform/ax_platform_node_textchildprovider_win.h
index 029516d8..e770ae75 100644
--- a/ui/accessibility/platform/ax_platform_node_textchildprovider_win.h
+++ b/ui/accessibility/platform/ax_platform_node_textchildprovider_win.h
@@ -5,10 +5,11 @@
 #ifndef UI_ACCESSIBILITY_PLATFORM_AX_PLATFORM_NODE_TEXTCHILDPROVIDER_WIN_H_
 #define UI_ACCESSIBILITY_PLATFORM_AX_PLATFORM_NODE_TEXTCHILDPROVIDER_WIN_H_
 
+#include "ui/accessibility/ax_export.h"
 #include "ui/accessibility/platform/ax_platform_node_win.h"
 
 namespace ui {
-class AXPlatformNodeTextChildProviderWin
+class AX_EXPORT AXPlatformNodeTextChildProviderWin
     : public CComObjectRootEx<CComMultiThreadModel>,
       public ITextChildProvider {
  public:
diff --git a/ui/accessibility/platform/ax_platform_node_textchildprovider_win_unittest.cc b/ui/accessibility/platform/ax_platform_node_textchildprovider_win_unittest.cc
index 37bf56a1..91f250c 100644
--- a/ui/accessibility/platform/ax_platform_node_textchildprovider_win_unittest.cc
+++ b/ui/accessibility/platform/ax_platform_node_textchildprovider_win_unittest.cc
@@ -5,9 +5,9 @@
 #include "ui/accessibility/platform/ax_platform_node_win_unittest.h"
 
 #include "ui/accessibility/platform/ax_fragment_root_win.h"
-#include "ui/accessibility/platform/ax_platform_node_textchildprovider_win.cc"
-#include "ui/accessibility/platform/ax_platform_node_textprovider_win.cc"
-#include "ui/accessibility/platform/ax_platform_node_textrangeprovider_win.cc"
+#include "ui/accessibility/platform/ax_platform_node_textchildprovider_win.h"
+#include "ui/accessibility/platform/ax_platform_node_textprovider_win.h"
+#include "ui/accessibility/platform/ax_platform_node_textrangeprovider_win.h"
 
 using Microsoft::WRL::ComPtr;