Move PlatformBrowserTest alias to platform_browser_test.h

Currently, every test leveraging PlatformBrowserTest should include
the following if-def block:

```
#if BUILDFLAG(IS_ANDROID)
#include "chrome/test/base/android/android_browser_test.h"
#else
#include "chrome/test/base/in_process_browser_test.h"
#endif
```

And, in turn, PlatformBrowserTest is an alias for either
AndroidBrowserTest or InProcessBrowserTest, as defined in each of
those files.

This makes for a lot of boilerplate, and instead we can just move
that if-def'd alias to a single file, platform_browser_test.h, that
each class can include.

This CL makes the following changes:
- Updates any sites that previously included that if-def block to just
  include platform_browser_test.h
- Fixes many IWYU cases where classes were not properly including any
  header file
- `git cl format` (which fixes a few cases of improper header sorting)

Bug: 361002665
Change-Id: I07ffeaf1dc82e568d5c4e7bebe47c5b459afae64
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5794166
Commit-Queue: Devlin Cronin <[email protected]>
Reviewed-by: Erik Chen <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1345701}
diff --git a/chrome/browser/webaudio/webaudio_browsertest.cc b/chrome/browser/webaudio/webaudio_browsertest.cc
index ef95c09..17fa96e 100644
--- a/chrome/browser/webaudio/webaudio_browsertest.cc
+++ b/chrome/browser/webaudio/webaudio_browsertest.cc
@@ -4,16 +4,11 @@
 
 #include "build/build_config.h"
 #include "chrome/test/base/chrome_test_utils.h"
+#include "chrome/test/base/platform_browser_test.h"
 #include "content/public/test/browser_test.h"
 #include "content/public/test/browser_test_utils.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
-#if BUILDFLAG(IS_ANDROID)
-#include "chrome/test/base/android/android_browser_test.h"
-#else
-#include "chrome/test/base/in_process_browser_test.h"
-#endif
-
 // TODO(crbug.com/40167066): Investigate why different macOS versions have
 // different fingerprints.
 #if BUILDFLAG(IS_MAC)