Move kMediaStreamSource* constants to blink_common.dll

kMediaStreamSourceTab, kMediaStreamSourceScreen,
kMediaStreamSourceDesktop and kMediaStreamSourceSystem were
declared to be exported from both blink_platform.dll and
blink_common.dll. In some build configurations that
inconsistency caused build errors:

In file included from third_party/blink/renderer/platform/mediastream/media_stream_center.cc:42:
In file included from third_party/blink/renderer/platform/mediastream/media_stream_descriptor.h:37:
In file included from third_party/blink/renderer/platform/mediastream/media_stream_source.h:39:
In file included from third_party/blink/public/platform/modules/mediastream/web_platform_media_stream_source.h:9:
../..\third_party/blink/public/common/mediastream/media_stream_controls.h(17,1): error: 'dllimport' attribute ignored [-Werror,-Wignored-attributes]
BLINK_COMMON_EXPORT extern const char kMediaStreamSourceTab[];

The error is triggered by first seeing the constant with a
declspec(dllexport) (expanded from BLINK_PLATFORM_EXPORT) and
then with a declspec(dllimport) (expanded from
BLINK_COMMON_EXPORT).

Since common can't depend on platform, the constants need to be
in blink_common.dll so this moves them there.

This is only an issue in Windows component builds.

Bug: 704136
Change-Id: I4bcd6c5b29e534ecfc3ffef908a095b2d33f3a44
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1729251Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Daniel Bratell <bratell@opera.com>
Auto-Submit: Daniel Bratell <bratell@opera.com>
Cr-Commit-Position: refs/heads/master@{#682732}

third_party/blink/common/mediastream/media_stream_controls.cc

@@ -6,6 +6,11 @@
 
 namespace blink {
 
+const char kMediaStreamSourceTab[] = "tab";
+const char kMediaStreamSourceScreen[] = "screen";
+const char kMediaStreamSourceDesktop[] = "desktop";
+const char kMediaStreamSourceSystem[] = "system";
+
 TrackControls::TrackControls() {}
 
 TrackControls::TrackControls(bool request, mojom::MediaStreamType type)

third_party/blink/public/platform/modules/mediastream/web_platform_media_stream_source.h

@@ -6,6 +6,7 @@
 #define THIRD_PARTY_BLINK_PUBLIC_PLATFORM_MODULES_MEDIASTREAM_WEB_PLATFORM_MEDIA_STREAM_SOURCE_H_
 
 #include "base/callback.h"
+#include "third_party/blink/public/common/mediastream/media_stream_controls.h"
 #include "third_party/blink/public/common/mediastream/media_stream_request.h"
 #include "third_party/blink/public/mojom/mediastream/media_stream.mojom-shared.h"
 #include "third_party/blink/public/platform/web_common.h"
@@ -17,15 +18,6 @@ namespace blink {
 class MediaStreamSource;
 class WebMediaStreamSource;
 
-// Names for media stream source capture types.
-// These are values set via the "chromeMediaSource" constraint.
-BLINK_PLATFORM_EXPORT extern const char kMediaStreamSourceTab[];
-BLINK_PLATFORM_EXPORT extern const char
-    kMediaStreamSourceScreen[]; /* video only */
-BLINK_PLATFORM_EXPORT extern const char kMediaStreamSourceDesktop[];
-BLINK_PLATFORM_EXPORT extern const char
-    kMediaStreamSourceSystem[]; /* audio only */
-
 class BLINK_PLATFORM_EXPORT WebPlatformMediaStreamSource {
  public:
   using SourceStoppedCallback =

third_party/blink/renderer/platform/exported/mediastream/web_platform_media_stream_source.cc

@@ -11,11 +11,6 @@
 
 namespace blink {
 
-const char kMediaStreamSourceTab[] = "tab";
-const char kMediaStreamSourceScreen[] = "screen";
-const char kMediaStreamSourceDesktop[] = "desktop";
-const char kMediaStreamSourceSystem[] = "system";
-
 const char WebPlatformMediaStreamSource::kSourceId[] = "sourceId";
 
 WebPlatformMediaStreamSource::WebPlatformMediaStreamSource() {}