Android: Update android studio instructions

Native files require all variants to be synced with gradle. Thus we must
turn off "only sync active variant" optimization in newer Android Studio
versions.

Also add instructions for handling AndroidManifest.xml errors.

Bug: 620034, 917016
Change-Id: I00370328226c6cfe05de02f08188d74c32e97056
Reviewed-on: https://chromium-review.googlesource.com/c/1398396
Reviewed-by: Justin DeWitt <dewittj@chromium.org>
Commit-Queue: Peter Wen <wnwen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#621212}

docs/android_studio.md

@@ -11,10 +11,6 @@ Make sure you have followed
 build/android/gradle/generate_gradle.py --output-directory out/Debug
 ```
 
-```shell
-build/android/gradle/generate_gradle.py --output-directory out/Debug --sdk AndroidStudioDefault
-```
-
 The above commands create a project dir `gradle` under your output directory.
 Use `--project-dir <project-dir>` to change this.
 
@@ -25,14 +21,9 @@ To import the project:
 See [android_test_instructions.md](android_test_instructions.md#Using-Emulators)
 for more information about building and running emulators.
 
-If you're asked to use Studio's Android SDK:
-* No.
-    * Selecting No ensures that the SDK used by Android Studio is the same as
-      the one set by `generate_gradle.py`. If you want a different SDK pass
-      `--sdk` to `generate_gradle.py`.
+If you're asked to use Studio's Android SDK: No.
 
-If you're asked to use Studio's Gradle wrapper:
-* Yes.
+If you're asked to use Studio's Gradle wrapper: Yes.
 
 You need to re-run `generate_gradle.py` whenever `BUILD.gn` files change.
 
@@ -89,11 +80,15 @@ in order to try it out. The target must be the full path and name of a valid gn
 target (no shorthands). This will require you to install `cmake` and `ndk` when
 prompted. Accept Android Studio's prompts for these SDK packages.
 
+You need to disable a new gradle option in order to edit native files:
+File -&gt; Settings -&gt; Experimental
+-&gt; Gradle and uncheck "Only resolve selected variants".
+
 This is not necessary, but to avoid "This file is not part of the project...",
 you can either add an extra `--native-target` flag or simply copy and paste the
 absolute path to that file into the CMakeLists.txt file alongside the existing
-file paths. Note that these changes will be overwritten on your next invocation
-of `generate_gradle.py`.
+file paths. Note that changes to CMakeLists.txt will be overwritten on your next
+invocation of `generate_gradle.py`.
 
 Example: