IWYU: std::unordered_map with value type OptimizationGuideNavigationData...

IWYU: std::unordered_map with value type OptimizationGuideNavigationData requires that type declaration

Fix compilation in GNU stdc++ due to missing declaration of the full type:
    ../../chrome/browser/optimization_guide/optimization_guide_web_contents_observer.h:22:7: note: forward declaration of ‘class OptimizationGuideNavigationData’
    class OptimizationGuideNavigationData;
          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Bug: 957519
Change-Id: I9d792c0f288d6544e10cd419adf4d845535aaea9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1768337Reviewed-by: rajendrant <rajendrant@chromium.org>
Commit-Queue: José Dapena Paz <jose.dapena@lge.com>
Cr-Commit-Position: refs/heads/master@{#690312}

chrome/browser/optimization_guide/optimization_guide_web_contents_observer.cc

@@ -7,7 +7,6 @@
 #include "base/base64.h"
 #include "chrome/browser/optimization_guide/optimization_guide_keyed_service.h"
 #include "chrome/browser/optimization_guide/optimization_guide_keyed_service_factory.h"
-#include "chrome/browser/optimization_guide/optimization_guide_navigation_data.h"
 #include "chrome/browser/profiles/profile.h"
 #include "components/optimization_guide/hints_fetcher.h"
 #include "components/optimization_guide/optimization_guide_features.h"

chrome/browser/optimization_guide/optimization_guide_web_contents_observer.h

@@ -11,6 +11,7 @@
 
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
+#include "chrome/browser/optimization_guide/optimization_guide_navigation_data.h"
 #include "content/public/browser/web_contents_observer.h"
 #include "content/public/browser/web_contents_user_data.h"
 
@@ -19,7 +20,6 @@ class NavigationHandle;
 }  // namespace content
 
 class OptimizationGuideKeyedService;
-class OptimizationGuideNavigationData;
 
 // Observes navigation events.
 class OptimizationGuideWebContentsObserver