Trigger font scanning at browser startup, not lazily on demand

Since font scanning is now an asynchronous, BEST_EFFORT priority task,
we should trigger it at startup so it may already be ready when a
renderer requests it. Previously, it was a synchronous task, triggered
by when a renderer requested the lookup table for the first
time. Triggering it at startup matches the approach we take on Windows 7
and 8.

Bug: 973394
Change-Id: I2e890058c538ed157217e98d1f4a0bdba639a602
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1681760Reviewed-by: Avi Drissman <avi@chromium.org>
Commit-Queue: Dominik Röttsches <drott@chromium.org>
Cr-Commit-Position: refs/heads/master@{#673386}

content/browser/browser_main_loop.cc

@@ -165,6 +165,7 @@
 #include "content/browser/android/launcher_thread.h"
 #include "content/browser/android/scoped_surface_request_manager.h"
 #include "content/browser/android/tracing_controller_android.h"
+#include "content/browser/font_unique_name_lookup/font_unique_name_lookup.h"
 #include "content/browser/screen_orientation/screen_orientation_delegate_android.h"
 #include "media/base/android/media_drm_bridge_client.h"
 #include "ui/android/screen_android.h"
@@ -1433,6 +1434,9 @@ int BrowserMainLoop::BrowserThreadsStarted() {
 
 #if defined(OS_ANDROID)
   media::SetMediaDrmBridgeClient(GetContentClient()->GetMediaDrmBridgeClient());
+  if (base::FeatureList::IsEnabled(features::kFontSrcLocalMatching)) {
+    FontUniqueNameLookup::GetInstance();
+  }
 #endif
 
 #if defined(ENABLE_IPC_FUZZER)

content/browser/font_unique_name_lookup/font_unique_name_lookup.h

@@ -30,11 +30,12 @@ class CONTENT_EXPORT FontUniqueNameLookup {
  public:
   FontUniqueNameLookup() = delete;
 
-  // Retrieve an initialized instance of FontUniqueNameLookup that has read the
-  // table from cache if there was one, updated the lookup table if needed
-  // (i.e. if there was an Android firmware update) from the standard Android
-  // font directories, and written the updated lookup table back to file. It is
-  // ready to use with FontTableMatcher.
+  // Retrieve an instance of FontUniqueNameLookup. On the first call to
+  // GetInstance() this that will start a task reading the lookup table from
+  // cache if there was a cached one, updating the lookup table if needed
+  // (i.e. if there was an Android firmware update or no cached one existed)
+  // from the standard Android font directories, and writing the updated lookup
+  // table back to file.
   static FontUniqueNameLookup& GetInstance();
 
   // Construct a FontUniqueNameLookup given a cache directory path