Improve error msg in CronetBufferedOutputStream

Bug: 874152
Cq-Include-Trybots: master.tryserver.chromium.android:android_cronet_tester
Change-Id: I45441e5fdd8eaa4b0e39144cd94d610d3f98f368
Reviewed-on: https://chromium-review.googlesource.com/1174935
Commit-Queue: Paul Jensen <pauljensen@chromium.org>
Reviewed-by: Paul Jensen <pauljensen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#583240}

components/cronet/android/java/src/org/chromium/net/urlconnection/CronetBufferedOutputStream.java

@@ -94,7 +94,8 @@ final class CronetBufferedOutputStream extends CronetOutputStream {
                     + mInitialContentLength + " bytes");
         }
         if (mConnected) {
-            throw new IllegalStateException("Cannot write after being connected.");
+            throw new IllegalStateException("Use setFixedLengthStreamingMode() or "
+                    + "setChunkedStreamingMode() for writing after connect");
         }
         if (mInitialContentLength != -1) {
             // If mInitialContentLength is known, the buffer should not grow.

components/cronet/android/test/javatests/src/org/chromium/net/urlconnection/CronetBufferedOutputStreamTest.java

@@ -92,7 +92,9 @@ public class CronetBufferedOutputStreamTest {
             out.write(TestUtil.UPLOAD_DATA);
             fail();
         } catch (IllegalStateException e) {
-            assertEquals("Cannot write after being connected.", e.getMessage());
+            assertEquals("Use setFixedLengthStreamingMode() or "
+                            + "setChunkedStreamingMode() for writing after connect",
+                    e.getMessage());
         }
     }