[jumbo] avoid operator clashes between media_devices.h and page_state.h

CL https://chromium-review.googlesource.com/c/chromium/src/+/1019245 seems
to have introduced a jumbo build failure:

./../../content/browser/renderer_host/media/media_devices_manager.cc:704:37: error: reference to overloaded function could not be resolved; did you mean to call it?
                  ignore_group_id ? operator== : EqualDeviceAndGroupID)) {
                                    ^~~~~~~~~~
../../content/common/media/media_devices.h:52:6: note: possible target for call
bool operator==(const MediaDeviceInfo& first, const MediaDeviceInfo& second);
     ^
../../content/public/common/page_state.h:63:13: note: possible target for call
inline bool operator==(const PageState& a, const PageState& b) {
            ^

Let's move page_state.h's ==/!= operators out of the global scope, to avoid this.

[email protected]

Bug: 834281
Change-Id: I27f0493ee2d2957b8318c969edd5615ec4dab687
Reviewed-on: https://chromium-review.googlesource.com/1042308
Commit-Queue: Morten Stenshorne <[email protected]>
Reviewed-by: Guido Urdaneta <[email protected]>
Cr-Commit-Position: refs/heads/master@{#555767}

content/public/common/page_state.h

@@ -53,20 +53,18 @@ class CONTENT_EXPORT PageState {
   PageState RemoveScrollOffset() const;
   PageState RemoveReferrer() const;
 
+  // Support DCHECK_EQ(a, b), etc.
+  bool operator==(const PageState& other) const { return this->Equals(other); }
+  bool operator!=(const PageState& other) const {
+    return !(this->Equals(other));
+  }
+
  private:
   PageState(const std::string& data);
 
   std::string data_;
 };
 
-// Support DCHECK_EQ(a, b), etc.
-inline bool operator==(const PageState& a, const PageState& b) {
-  return a.Equals(b);
-}
-inline bool operator!=(const PageState& a, const PageState& b) {
-  return !(a == b);
-}
-
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_COMMON_PAGE_STATE_H_