Move UKM PageLoad SourceId generation to PageLoadTracker.

chrome/browser/page_load_metrics/page_load_metrics_observer.h

Index: chrome/browser/page_load_metrics/page_load_metrics_observer.h
diff --git a/chrome/browser/page_load_metrics/page_load_metrics_observer.h b/chrome/browser/page_load_metrics/page_load_metrics_observer.h
index abd5ffaef8718aedb971b6cf384c055f77f5c0b9..04185b933286403c12d0aeb9163954e75801bc1d 100644
--- a/chrome/browser/page_load_metrics/page_load_metrics_observer.h
+++ b/chrome/browser/page_load_metrics/page_load_metrics_observer.h
@@ -12,6 +12,7 @@
 #include "base/optional.h"
 #include "chrome/common/page_load_metrics/page_load_timing.h"
 #include "components/data_reduction_proxy/core/browser/data_reduction_proxy_data.h"
+#include "components/ukm/ukm_source.h"
 #include "content/public/browser/navigation_handle.h"
 #include "content/public/browser/web_contents_observer.h"
 #include "content/public/common/resource_type.h"
@@ -123,7 +124,8 @@ struct PageLoadExtraInfo {
       UserInitiatedInfo page_end_user_initiated_info,
       const base::Optional<base::TimeDelta>& page_end_time,
       const mojom::PageLoadMetadata& main_frame_metadata,
-      const mojom::PageLoadMetadata& subframe_metadata);
+      const mojom::PageLoadMetadata& subframe_metadata,
+      ukm::SourceId source_id);
 
   // Simplified version of the constructor, intended for use in tests.
   static PageLoadExtraInfo CreateForTesting(const GURL& url,
@@ -196,6 +198,9 @@ struct PageLoadExtraInfo {
 
   // PageLoadMetadata for subframes of the current page load.
   const mojom::PageLoadMetadata subframe_metadata;
+
+  // UKM SourceId for the current page load.
+  const ukm::SourceId source_id;
 };
 
 // Container for various information about a completed request within a page
@@ -274,6 +279,8 @@ class PageLoadMetricsObserver {
 
   virtual ~PageLoadMetricsObserver() {}
 
+  static bool IsStandardWebPageMimeType(const std::string& mime_type);
+
   // The page load started, with the given navigation handle.
   // currently_committed_url contains the URL of the committed page load at the
   // time the navigation for navigation_handle was initiated, or the empty URL
@@ -296,7 +303,8 @@ class PageLoadMetricsObserver {
   // reference to it.
   // Observers that return STOP_OBSERVING will not receive any additional
   // callbacks, and will be deleted after invocation of this method returns.
-  virtual ObservePolicy OnCommit(content::NavigationHandle* navigation_handle);
+  virtual ObservePolicy OnCommit(content::NavigationHandle* navigation_handle,
+                                 ukm::SourceId source_id);
 
   // OnDidFinishSubFrameNavigation is triggered when a sub-frame of the
   // committed page has finished navigating. It has either committed, aborted,