Android: use grit target platform instead of define.

chrome/renderer/resources/plugin_placeholders.css

Index: chrome/renderer/resources/plugin_placeholders.css
diff --git a/chrome/renderer/resources/plugin_placeholders.css b/chrome/renderer/resources/plugin_placeholders.css
index 84e66d767ebc96519b1095aebed57bb53ac9ea4d..0df42885f04b7ce8533a5265e3d8f4bdb85b2cfe 100644
--- a/chrome/renderer/resources/plugin_placeholders.css
+++ b/chrome/renderer/resources/plugin_placeholders.css
@@ -14,7 +14,7 @@ h1 {
   font-size: 10pt;
   font-weight: normal;
   padding: 0pt 10pt;
-<if expr="not pp_ifdef('android') and not pp_ifdef('chromeos')">
+<if expr="not is_android and not pp_ifdef('chromeos')">
   visibility: hidden;
 </if>
 }
@@ -41,16 +41,16 @@ p {
   height: 100%;
   width: 100%;
   top: 50%;
-<if expr="not pp_ifdef('android')">
+<if expr="not is_android">
   margin-top: -70px;
 </if>
-<if expr="pp_ifdef('android')">
+<if expr="is_android">
   margin-top: -14px;
 </if>
 }
 
 #close {
-<if expr="not pp_ifdef('android')">
+<if expr="not is_android">
   visibility: hidden;
 </if>
   cursor: pointer;