Remove android_webview_build completely.

tools/gn/docs/cookbook.md

 # GYP->GN Conversion Cookbook
 
 [TOC]
 
 ## Targets
 
 | *GYP*                                            | *GN*                                               |
 |:-------------------------------------------------|:---------------------------------------------------|
 | `'type': 'static_library', 'name': 'foo',`       | `static_library("foo") {` or `source_set("foo") {` |
 | `'type': 'shared_library', 'name': 'foo',`       | `shared_library("foo") {`                          |
@@ skipping 144 matching lines @@
   # ...
 }
 ```
 
 Other flags only apply to one `BUILD.gn` file and those flags are
 declared directly in that file (so other files can't use them). These
 places are noted in the table below.
 
 | *GYP*                                           | *GN*                                       | *GN import*                                    |
 |:------------------------------------------------|:-------------------------------------------|:-----------------------------------------------|
-| `android_src`                                   | `android_src`                              | `//build/config/android/config.gni`            |
-| `android_webview_build` (0/1)                   | `is_android_webview_build` (true/false)    | `//build/config/android/config.gni`            |
 | `arm_float_abi`                                 | `arm_float_abi`                            | `//build/config/arm.gni`                       |
 | `arm_neon` (0/1)                                | `arm_use_neon` (true/false)                | `//build/config/arm.gni`                       |
 | `arm_neon_optional` (0/1)                       | `arm_optionally_use_neon` (true/false)     | `//build/config/arm.gni`                       |
 | `arm_version`                                   | `arm_version`                              | `//build/config/arm.gni`                       |
 | `asan` (0/1)                                    | `is_asan` (true/false)                     | (global)                                       |
 | `branding` ("Chromium"/"Chrome"")               | `is_chrome_branded` (true/false)           | (global)                                       |
 | `build_for_tool=="drmemory"`                    | `disable_iterator_debugging` (true/false)  | (internal to `//build/config/BUILD.gn`)        |
 | `build_for_tool=="tsan"`                        | `disable_iterator_debugging` (true/false)  | (internal to `//build/config/BUILD.gn`)        |
 | `buildtype` ("Official"/"Dev")                  | `is_official_build` (true/false)           | (global)                                       |
 | `clang` (0/1)                                   | `is_clang` (true/false)                    | (global)                                       |
@@ skipping 467 matching lines @@
 
 ```
 import("//mojo/public/tools/bindings/mojom.gni")
 
 mojom("mojo_bindings") {
   sources = [
     "foo.mojom",
   ]
 }
 ```